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 $241.55   7.699%   $260.1469   $260.15   $260.15   $260.10  
  Purchase #2 $90.95   13.347%   $103.0891   $103.09   $103.10   $103.10  
  Purchase #3 $209.99   6.134%   $222.8708   $222.87   $222.85   $222.90  
  Purchase #4 $147.67   13.730%   $167.9451   $167.95   $167.95   $167.90  
  Purchase #5 $119.54   6.133%   $126.8714   $126.87   $126.85   $126.90  
  Purchase #6 $103.90   13.145%   $117.5577   $117.56   $117.55   $117.60  
  Purchase #7 $146.87   10.235%   $161.9021   $161.90   $161.90   $161.90  
  7 purchase totals = $1,060.47       $1,160.3831   $1,160.39   $1,160.35   $1,160.40