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 $57.35   5.710%   $60.6247   $60.62   $60.60   $60.60  
  Purchase #2 $73.55   13.428%   $83.4263   $83.43   $83.45   $83.40  
  Purchase #3 $178.36   13.500%   $202.4386   $202.44   $202.45   $202.40  
  Purchase #4 $27.34   7.447%   $29.376   $29.38   $29.40   $29.40  
  Purchase #5 $78.36   6.160%   $83.187   $83.19   $83.20   $83.20  
  Purchase #6 $196.98   13.597%   $223.7634   $223.76   $223.75   $223.80  
  Purchase #7 $38.98   11.194%   $43.3434   $43.34   $43.35   $43.30  
  7 purchase totals = $650.92       $726.1594   $726.16   $726.20   $726.10