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 $34.82   3.534%   $36.0505   $36.05   $36.05   $36.10  
  Purchase #2 $44.52   5.584%   $47.006   $47.01   $47.00   $47.00  
  Purchase #3 $115.75   13.189%   $131.0163   $131.02   $131.00   $131.00  
  Purchase #4 $177.34   9.699%   $194.5402   $194.54   $194.55   $194.50  
  Purchase #5 $26.97   12.111%   $30.2363   $30.24   $30.25   $30.20  
  Purchase #6 $8.84   10.259%   $9.7469   $9.75   $9.75   $9.70  
  Purchase #7 $127.37   7.190%   $136.5279   $136.53   $136.55   $136.50  
  7 purchase totals = $535.61       $585.1241   $585.14   $585.15   $585.00