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 $117.72   6.320%   $125.1599   $125.16   $125.15   $125.20  
  Purchase #2 $204.51   9.832%   $224.6174   $224.62   $224.60   $224.60  
  Purchase #3 $123.35   13.228%   $139.6667   $139.67   $139.65   $139.70  
  Purchase #4 $198.66   8.834%   $216.2096   $216.21   $216.20   $216.20  
  Purchase #5 $61.74   7.768%   $66.536   $66.54   $66.55   $66.50  
  Purchase #6 $230.65   7.443%   $247.8173   $247.82   $247.80   $247.80  
  Purchase #7 $210.54   3.166%   $217.2057   $217.21   $217.20   $217.20  
  7 purchase totals = $1,147.17       $1,237.2126   $1,237.23   $1,237.15   $1,237.20