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 $58.59   5.506%   $61.816   $61.82   $61.80   $61.80  
  Purchase #2 $114.86   12.258%   $128.9395   $128.94   $128.95   $128.90  
  Purchase #3 $8.63   7.663%   $9.2913   $9.29   $9.30   $9.30  
  Purchase #4 $69.60   5.188%   $73.2108   $73.21   $73.20   $73.20  
  Purchase #5 $144.32   10.556%   $159.5544   $159.55   $159.55   $159.60  
  Purchase #6 $249.43   10.572%   $275.7997   $275.80   $275.80   $275.80  
  Purchase #7 $146.47   12.122%   $164.2251   $164.23   $164.25   $164.20  
  7 purchase totals = $791.90       $872.8368   $872.84   $872.85   $872.80