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 $83.82   13.171%   $94.8599   $94.86   $94.85   $94.90  
  Purchase #2 $238.35   10.411%   $263.1646   $263.16   $263.15   $263.20  
  Purchase #3 $236.75   5.403%   $249.5416   $249.54   $249.55   $249.50  
  Purchase #4 $209.64   4.670%   $219.4302   $219.43   $219.45   $219.40  
  Purchase #5 $109.51   10.775%   $121.3097   $121.31   $121.30   $121.30  
  Purchase #6 $159.54   6.866%   $170.494   $170.49   $170.50   $170.50  
  Purchase #7 $107.83   13.304%   $122.1757   $122.18   $122.20   $122.20  
  7 purchase totals = $1,145.44       $1,240.9757   $1,240.97   $1,241.00   $1,241.00