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 $171.36   13.518%   $194.5244   $194.52   $194.50   $194.50  
  Purchase #2 $239.53   9.328%   $261.8734   $261.87   $261.85   $261.90  
  Purchase #3 $64.67   13.505%   $73.4037   $73.40   $73.40   $73.40  
  Purchase #4 $242.35   9.656%   $265.7513   $265.75   $265.75   $265.80  
  Purchase #5 $68.45   5.590%   $72.2764   $72.28   $72.30   $72.30  
  Purchase #6 $189.79   5.297%   $199.8432   $199.84   $199.85   $199.80  
  Purchase #7 $6.62   13.672%   $7.5251   $7.53   $7.55   $7.50  
  7 purchase totals = $982.77       $1,075.1975   $1,075.19   $1,075.20   $1,075.20