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 $118.61   6.392%   $126.1916   $126.19   $126.20   $126.20  
  Purchase #2 $158.25   5.168%   $166.4284   $166.43   $166.45   $166.40  
  Purchase #3 $187.29   5.390%   $197.3849   $197.38   $197.40   $197.40  
  Purchase #4 $54.59   6.631%   $58.2099   $58.21   $58.20   $58.20  
  Purchase #5 $151.80   13.342%   $172.0532   $172.05   $172.05   $172.10  
  Purchase #6 $73.71   7.561%   $79.2832   $79.28   $79.30   $79.30  
  Purchase #7 $186.87   7.736%   $201.3263   $201.33   $201.35   $201.30  
  7 purchase totals = $931.12       $1,000.8775   $1,000.87   $1,000.95   $1,000.90