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 $98.46   3.539%   $101.9445   $101.94   $101.95   $101.90  
  Purchase #2 $69.72   9.285%   $76.1935   $76.19   $76.20   $76.20  
  Purchase #3 $119.36   9.380%   $130.556   $130.56   $130.55   $130.60  
  Purchase #4 $94.73   8.204%   $102.5016   $102.50   $102.50   $102.50  
  Purchase #5 $98.33   7.486%   $105.691   $105.69   $105.70   $105.70  
  Purchase #6 $87.61   11.124%   $97.3557   $97.36   $97.35   $97.40  
  Purchase #7 $59.60   10.442%   $65.8234   $65.82   $65.80   $65.80  
  7 purchase totals = $627.81       $680.0657   $680.06   $680.05   $680.10