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 $110.87   8.412%   $120.1964   $120.20   $120.20   $120.20  
  Purchase #2 $73.88   4.575%   $77.26   $77.26   $77.25   $77.30  
  Purchase #3 $250.87   9.408%   $274.4718   $274.47   $274.45   $274.50  
  Purchase #4 $131.88   4.453%   $137.7526   $137.75   $137.75   $137.80  
  Purchase #5 $201.62   12.688%   $227.2015   $227.20   $227.20   $227.20  
  Purchase #6 $221.49   11.607%   $247.1983   $247.20   $247.20   $247.20  
  Purchase #7 $84.96   9.707%   $93.2071   $93.21   $93.20   $93.20  
  7 purchase totals = $1,075.57       $1,177.2877   $1,177.29   $1,177.25   $1,177.40