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 $93.90   8.320%   $101.7125   $101.71   $101.70   $101.70  
  Purchase #2 $194.87   3.638%   $201.9594   $201.96   $201.95   $202.00  
  Purchase #3 $17.77   13.353%   $20.1428   $20.14   $20.15   $20.10  
  Purchase #4 $247.85   3.790%   $257.2435   $257.24   $257.25   $257.20  
  Purchase #5 $79.68   10.213%   $87.8177   $87.82   $87.80   $87.80  
  Purchase #6 $7.64   11.609%   $8.5269   $8.53   $8.55   $8.50  
  Purchase #7 $94.87   8.295%   $102.7395   $102.74   $102.75   $102.70  
  7 purchase totals = $736.58       $780.1423   $780.14   $780.15   $780.00