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 $241.82   7.350%   $259.5938   $259.59   $259.60   $259.60  
  Purchase #2 $235.61   10.767%   $260.9781   $260.98   $261.00   $261.00  
  Purchase #3 $169.33   7.455%   $181.9536   $181.95   $181.95   $182.00  
  Purchase #4 $150.67   12.568%   $169.6062   $169.61   $169.60   $169.60  
  Purchase #5 $148.89   9.434%   $162.9363   $162.94   $162.95   $162.90  
  Purchase #6 $191.40   9.224%   $209.0547   $209.05   $209.05   $209.10  
  Purchase #7 $39.70   9.679%   $43.5426   $43.54   $43.55   $43.50  
  7 purchase totals = $1,177.42       $1,287.6653   $1,287.66   $1,287.70   $1,287.70