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 $182.45   8.140%   $197.3014   $197.30   $197.30   $197.30  
  Purchase #2 $136.77   7.450%   $146.9594   $146.96   $146.95   $147.00  
  Purchase #3 $60.27   7.202%   $64.6106   $64.61   $64.60   $64.60  
  Purchase #4 $63.42   4.684%   $66.3906   $66.39   $66.40   $66.40  
  Purchase #5 $207.49   5.570%   $219.0472   $219.05   $219.05   $219.00  
  Purchase #6 $144.51   9.423%   $158.1272   $158.13   $158.15   $158.10  
  Purchase #7 $190.50   6.122%   $202.1624   $202.16   $202.15   $202.20  
  7 purchase totals = $985.41       $1,054.5988   $1,054.60   $1,054.60   $1,054.60