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 $65.82   9.679%   $72.1907   $72.19   $72.20   $72.20  
  Purchase #2 $97.67   13.208%   $110.5703   $110.57   $110.55   $110.60  
  Purchase #3 $144.80   11.140%   $160.9307   $160.93   $160.95   $160.90  
  Purchase #4 $159.72   3.828%   $165.8341   $165.83   $165.85   $165.80  
  Purchase #5 $14.77   9.653%   $16.1957   $16.20   $16.20   $16.20  
  Purchase #6 $228.86   13.634%   $260.0628   $260.06   $260.05   $260.10  
  Purchase #7 $200.42   4.610%   $209.6594   $209.66   $209.65   $209.70  
  7 purchase totals = $912.06       $995.4437   $995.44   $995.45   $995.50