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 $82.69   13.370%   $93.7457   $93.75   $93.75   $93.70  
  Purchase #2 $144.98   13.791%   $164.9742   $164.97   $164.95   $165.00  
  Purchase #3 $150.94   10.351%   $166.5638   $166.56   $166.55   $166.60  
  Purchase #4 $27.34   9.445%   $29.9223   $29.92   $29.90   $29.90  
  Purchase #5 $156.86   6.185%   $166.5618   $166.56   $166.55   $166.60  
  Purchase #6 $207.87   11.720%   $232.2324   $232.23   $232.25   $232.20  
  Purchase #7 $23.91   12.321%   $26.856   $26.86   $26.85   $26.90  
  7 purchase totals = $794.59       $880.8562   $880.85   $880.80   $880.90