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 $167.97   8.234%   $181.8006   $181.80   $181.80   $181.80  
  Purchase #2 $198.75   4.424%   $207.5427   $207.54   $207.55   $207.50  
  Purchase #3 $44.76   11.555%   $49.932   $49.93   $49.95   $49.90  
  Purchase #4 $29.91   11.526%   $33.3574   $33.36   $33.35   $33.40  
  Purchase #5 $165.89   10.133%   $182.6996   $182.70   $182.70   $182.70  
  Purchase #6 $176.47   12.148%   $197.9076   $197.91   $197.90   $197.90  
  Purchase #7 $239.35   5.817%   $253.273   $253.27   $253.25   $253.30  
  7 purchase totals = $1,023.10       $1,106.5129   $1,106.51   $1,106.50   $1,106.50