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 $36.37   12.758%   $41.0101   $41.01   $41.00   $41.00  
  Purchase #2 $167.43   11.442%   $186.5873   $186.59   $186.60   $186.60  
  Purchase #3 $40.92   4.616%   $42.8089   $42.81   $42.80   $42.80  
  Purchase #4 $243.52   6.249%   $258.7376   $258.74   $258.75   $258.70  
  Purchase #5 $234.71   5.503%   $247.6261   $247.63   $247.65   $247.60  
  Purchase #6 $156.74   5.837%   $165.8889   $165.89   $165.90   $165.90  
  Purchase #7 $238.73   9.556%   $261.543   $261.54   $261.55   $261.50  
  7 purchase totals = $1,118.42       $1,204.2019   $1,204.21   $1,204.25   $1,204.10