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 $163.73   12.770%   $184.6383   $184.64   $184.65   $184.60  
  Purchase #2 $192.33   13.531%   $218.3542   $218.35   $218.35   $218.40  
  Purchase #3 $183.92   8.711%   $199.9413   $199.94   $199.95   $199.90  
  Purchase #4 $67.92   6.798%   $72.5372   $72.54   $72.55   $72.50  
  Purchase #5 $237.94   11.304%   $264.8367   $264.84   $264.85   $264.80  
  Purchase #6 $76.67   10.589%   $84.7886   $84.79   $84.80   $84.80  
  Purchase #7 $38.33   7.802%   $41.3205   $41.32   $41.30   $41.30  
  7 purchase totals = $960.84       $1,066.4168   $1,066.42   $1,066.45   $1,066.30