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 $96.65   8.161%   $104.5376   $104.54   $104.55   $104.50  
  Purchase #2 $228.65   5.290%   $240.7456   $240.75   $240.75   $240.70  
  Purchase #3 $95.50   4.379%   $99.6819   $99.68   $99.70   $99.70  
  Purchase #4 $166.77   8.528%   $180.9921   $180.99   $181.00   $181.00  
  Purchase #5 $78.73   8.450%   $85.3827   $85.38   $85.40   $85.40  
  Purchase #6 $91.44   8.602%   $99.3057   $99.31   $99.30   $99.30  
  Purchase #7 $104.98   13.462%   $119.1124   $119.11   $119.10   $119.10  
  7 purchase totals = $862.72       $929.7580   $929.76   $929.80   $929.70