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 $53.36   6.414%   $56.7825   $56.78   $56.80   $56.80  
  Purchase #2 $27.46   7.611%   $29.55   $29.55   $29.55   $29.60  
  Purchase #3 $121.38   3.447%   $125.564   $125.56   $125.55   $125.60  
  Purchase #4 $24.85   5.185%   $26.1385   $26.14   $26.15   $26.10  
  Purchase #5 $100.41   9.518%   $109.967   $109.97   $109.95   $110.00  
  Purchase #6 $161.93   3.300%   $167.2737   $167.27   $167.25   $167.30  
  Purchase #7 $235.97   5.873%   $249.8285   $249.83   $249.85   $249.80  
  7 purchase totals = $725.36       $765.1042   $765.10   $765.10   $765.20