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 $236.62   5.385%   $249.362   $249.36   $249.35   $249.40  
  Purchase #2 $174.46   9.533%   $191.0913   $191.09   $191.10   $191.10  
  Purchase #3 $121.37   9.588%   $133.007   $133.01   $133.00   $133.00  
  Purchase #4 $146.46   13.413%   $166.1047   $166.10   $166.10   $166.10  
  Purchase #5 $184.30   3.166%   $190.1349   $190.13   $190.15   $190.10  
  Purchase #6 $239.44   9.844%   $263.0105   $263.01   $263.00   $263.00  
  Purchase #7 $204.80   12.668%   $230.7441   $230.74   $230.75   $230.70  
  7 purchase totals = $1,307.45       $1,423.4545   $1,423.44   $1,423.45   $1,423.40