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 $86.79   7.647%   $93.4268   $93.43   $93.45   $93.40  
  Purchase #2 $241.45   11.629%   $269.5282   $269.53   $269.55   $269.50  
  Purchase #3 $139.43   13.427%   $158.1513   $158.15   $158.15   $158.20  
  Purchase #4 $156.56   6.857%   $167.2953   $167.30   $167.30   $167.30  
  Purchase #5 $233.71   11.537%   $260.6731   $260.67   $260.65   $260.70  
  Purchase #6 $84.67   4.369%   $88.3692   $88.37   $88.35   $88.40  
  Purchase #7 $244.29   13.730%   $277.831   $277.83   $277.85   $277.80  
  7 purchase totals = $1,186.90       $1,315.2749   $1,315.28   $1,315.30   $1,315.30