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 $58.49   13.236%   $66.2317   $66.23   $66.25   $66.20  
  Purchase #2 $250.57   5.206%   $263.6147   $263.61   $263.60   $263.60  
  Purchase #3 $228.78   12.667%   $257.7596   $257.76   $257.75   $257.80  
  Purchase #4 $68.68   10.370%   $75.8021   $75.80   $75.80   $75.80  
  Purchase #5 $8.77   4.443%   $9.1597   $9.16   $9.15   $9.20  
  Purchase #6 $223.77   11.417%   $249.3178   $249.32   $249.30   $249.30  
  Purchase #7 $187.66   7.672%   $202.0573   $202.06   $202.05   $202.10  
  7 purchase totals = $1,026.72       $1,123.9429   $1,123.94   $1,123.90   $1,124.00