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 $60.91   6.134%   $64.6462   $64.65   $64.65   $64.60  
  Purchase #2 $30.87   13.218%   $34.9504   $34.95   $34.95   $35.00  
  Purchase #3 $93.48   11.855%   $104.5621   $104.56   $104.55   $104.60  
  Purchase #4 $24.31   6.186%   $25.8138   $25.81   $25.80   $25.80  
  Purchase #5 $234.42   11.135%   $260.5227   $260.52   $260.50   $260.50  
  Purchase #6 $71.93   6.453%   $76.5716   $76.57   $76.55   $76.60  
  Purchase #7 $127.70   7.331%   $137.0617   $137.06   $137.05   $137.10  
  7 purchase totals = $643.62       $704.1285   $704.12   $704.05   $704.20