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 $62.84   3.839%   $65.2524   $65.25   $65.25   $65.30  
  Purchase #2 $183.42   5.256%   $193.0606   $193.06   $193.05   $193.10  
  Purchase #3 $241.39   5.310%   $254.2078   $254.21   $254.20   $254.20  
  Purchase #4 $117.45   8.221%   $127.1056   $127.11   $127.10   $127.10  
  Purchase #5 $135.28   8.137%   $146.2877   $146.29   $146.30   $146.30  
  Purchase #6 $86.66   9.674%   $95.0435   $95.04   $95.05   $95.00  
  Purchase #7 $57.81   10.573%   $63.9223   $63.92   $63.90   $63.90  
  7 purchase totals = $884.85       $944.8799   $944.88   $944.85   $944.90