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 $235.61   9.352%   $257.6442   $257.64   $257.65   $257.60  
  Purchase #2 $86.46   9.508%   $94.6806   $94.68   $94.70   $94.70  
  Purchase #3 $185.82   9.647%   $203.7461   $203.75   $203.75   $203.70  
  Purchase #4 $96.71   7.802%   $104.2553   $104.26   $104.25   $104.30  
  Purchase #5 $59.77   10.129%   $65.8241   $65.82   $65.80   $65.80  
  Purchase #6 $104.52   12.700%   $117.794   $117.79   $117.80   $117.80  
  Purchase #7 $36.72   11.147%   $40.8132   $40.81   $40.80   $40.80  
  7 purchase totals = $805.61       $884.7575   $884.75   $884.75   $884.70