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 $64.98   10.640%   $71.8939   $71.89   $71.90   $71.90  
  Purchase #2 $94.39   7.705%   $101.6627   $101.66   $101.65   $101.70  
  Purchase #3 $112.36   8.331%   $121.7207   $121.72   $121.70   $121.70  
  Purchase #4 $130.52   13.568%   $148.229   $148.23   $148.25   $148.20  
  Purchase #5 $164.94   5.688%   $174.3218   $174.32   $174.30   $174.30  
  Purchase #6 $43.85   5.122%   $46.096   $46.10   $46.10   $46.10  
  Purchase #7 $182.42   11.459%   $203.3235   $203.32   $203.30   $203.30  
  7 purchase totals = $793.46       $867.2476   $867.24   $867.20   $867.20