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 $169.60   13.805%   $193.0133   $193.01   $193.00   $193.00  
  Purchase #2 $58.63   5.334%   $61.7573   $61.76   $61.75   $61.80  
  Purchase #3 $65.98   11.462%   $73.5426   $73.54   $73.55   $73.50  
  Purchase #4 $171.75   11.233%   $191.0427   $191.04   $191.05   $191.00  
  Purchase #5 $181.27   8.863%   $197.336   $197.34   $197.35   $197.30  
  Purchase #6 $93.68   12.429%   $105.3235   $105.32   $105.30   $105.30  
  Purchase #7 $159.97   8.616%   $173.753   $173.75   $173.75   $173.80  
  7 purchase totals = $900.88       $995.7684   $995.76   $995.75   $995.70