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 $22.58   6.193%   $23.9784   $23.98   $24.00   $24.00  
  Purchase #2 $165.78   8.744%   $180.2758   $180.28   $180.30   $180.30  
  Purchase #3 $31.55   10.357%   $34.8176   $34.82   $34.80   $34.80  
  Purchase #4 $82.25   13.421%   $93.2888   $93.29   $93.30   $93.30  
  Purchase #5 $178.63   5.715%   $188.8387   $188.84   $188.85   $188.80  
  Purchase #6 $179.35   12.380%   $201.5535   $201.55   $201.55   $201.60  
  Purchase #7 $132.86   6.132%   $141.007   $141.01   $141.00   $141.00  
  7 purchase totals = $793.00       $863.7598   $863.77   $863.80   $863.80