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 $52.88   12.772%   $59.6338   $59.63   $59.65   $59.60  
  Purchase #2 $41.44   3.197%   $42.7648   $42.76   $42.75   $42.80  
  Purchase #3 $68.86   6.829%   $73.5624   $73.56   $73.55   $73.60  
  Purchase #4 $236.98   12.632%   $266.9153   $266.92   $266.90   $266.90  
  Purchase #5 $96.77   10.600%   $107.0276   $107.03   $107.05   $107.00  
  Purchase #6 $193.73   8.292%   $209.7941   $209.79   $209.80   $209.80  
  Purchase #7 $179.40   10.273%   $197.8298   $197.83   $197.85   $197.80  
  7 purchase totals = $870.06       $957.5278   $957.52   $957.55   $957.50