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 $235.98   12.329%   $265.074   $265.07   $265.05   $265.10  
  Purchase #2 $86.76   9.676%   $95.1549   $95.15   $95.15   $95.20  
  Purchase #3 $97.94   7.683%   $105.4647   $105.46   $105.45   $105.50  
  Purchase #4 $129.75   9.666%   $142.2916   $142.29   $142.30   $142.30  
  Purchase #5 $25.25   11.617%   $28.1833   $28.18   $28.20   $28.20  
  Purchase #6 $142.52   4.209%   $148.5187   $148.52   $148.50   $148.50  
  Purchase #7 $86.67   10.728%   $95.968   $95.97   $95.95   $96.00  
  7 purchase totals = $804.87       $880.6552   $880.64   $880.60   $880.80