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 $58.60   11.466%   $65.3191   $65.32   $65.30   $65.30  
  Purchase #2 $168.72   7.105%   $180.7076   $180.71   $180.70   $180.70  
  Purchase #3 $92.30   10.671%   $102.1493   $102.15   $102.15   $102.10  
  Purchase #4 $232.61   5.820%   $246.1479   $246.15   $246.15   $246.10  
  Purchase #5 $65.69   10.779%   $72.7707   $72.77   $72.75   $72.80  
  Purchase #6 $123.84   12.465%   $139.2767   $139.28   $139.30   $139.30  
  Purchase #7 $155.49   5.283%   $163.7045   $163.70   $163.70   $163.70  
  7 purchase totals = $897.25       $970.0758   $970.08   $970.05   $970.00