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 $245.27   8.844%   $266.9617   $266.96   $266.95   $267.00  
  Purchase #2 $125.81   10.227%   $138.6766   $138.68   $138.70   $138.70  
  Purchase #3 $245.62   7.172%   $263.2359   $263.24   $263.25   $263.20  
  Purchase #4 $236.66   4.653%   $247.6718   $247.67   $247.65   $247.70  
  Purchase #5 $132.46   9.594%   $145.1682   $145.17   $145.15   $145.20  
  Purchase #6 $62.80   10.693%   $69.5152   $69.52   $69.50   $69.50  
  Purchase #7 $214.84   5.785%   $227.2685   $227.27   $227.25   $227.30  
  7 purchase totals = $1,263.46       $1,358.4979   $1,358.51   $1,358.45   $1,358.60