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 $58.87   6.487%   $62.6889   $62.69   $62.70   $62.70  
  Purchase #2 $188.98   7.799%   $203.7186   $203.72   $203.70   $203.70  
  Purchase #3 $5.68   9.469%   $6.2178   $6.22   $6.20   $6.20  
  Purchase #4 $236.87   12.853%   $267.3149   $267.31   $267.30   $267.30  
  Purchase #5 $210.34   11.845%   $235.2548   $235.25   $235.25   $235.30  
  Purchase #6 $179.68   6.400%   $191.1795   $191.18   $191.20   $191.20  
  Purchase #7 $24.65   7.582%   $26.519   $26.52   $26.50   $26.50  
  7 purchase totals = $905.07       $992.8935   $992.89   $992.85   $992.90