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 $58.30   6.537%   $62.1111   $62.11   $62.10   $62.10  
  Purchase #2 $236.87   8.680%   $257.4303   $257.43   $257.45   $257.40  
  Purchase #3 $232.54   6.151%   $246.8435   $246.84   $246.85   $246.80  
  Purchase #4 $98.30   9.120%   $107.265   $107.27   $107.25   $107.30  
  Purchase #5 $205.68   4.653%   $215.2503   $215.25   $215.25   $215.30  
  Purchase #6 $186.89   11.212%   $207.8441   $207.84   $207.85   $207.80  
  Purchase #7 $231.80   6.676%   $247.275   $247.28   $247.30   $247.30  
  7 purchase totals = $1,250.38       $1,344.0193   $1,344.02   $1,344.05   $1,344.00