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 $57.55   12.494%   $64.7403   $64.74   $64.75   $64.70  
  Purchase #2 $182.29   13.747%   $207.3494   $207.35   $207.35   $207.30  
  Purchase #3 $94.59   8.588%   $102.7134   $102.71   $102.70   $102.70  
  Purchase #4 $171.25   6.563%   $182.4891   $182.49   $182.50   $182.50  
  Purchase #5 $64.97   6.512%   $69.2008   $69.20   $69.20   $69.20  
  Purchase #6 $238.60   5.530%   $251.7946   $251.79   $251.80   $251.80  
  Purchase #7 $231.95   4.694%   $242.8377   $242.84   $242.85   $242.80  
  7 purchase totals = $1,041.20       $1,121.1253   $1,121.12   $1,121.15   $1,121.00