Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $144.64   12.825%   $163.1901   $163.19   $163.20   $163.20  
  Purchase #2 $232.58   7.338%   $249.6467   $249.65   $249.65   $249.60  
  Purchase #3 $186.34   7.296%   $199.9354   $199.94   $199.95   $199.90  
  Purchase #4 $173.53   13.787%   $197.4546   $197.45   $197.45   $197.50  
  Purchase #5 $96.50   12.619%   $108.6773   $108.68   $108.70   $108.70  
  Purchase #6 $163.80   8.709%   $178.0653   $178.07   $178.05   $178.10  
  Purchase #7 $152.32   9.803%   $167.2519   $167.25   $167.25   $167.30  
  7 purchase totals = $1,149.71       $1,264.2213   $1,264.23   $1,264.25   $1,264.30