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 $215.54   13.571%   $244.7909   $244.79   $244.80   $244.80  
  Purchase #2 $104.39   9.402%   $114.2047   $114.20   $114.20   $114.20  
  Purchase #3 $153.38   4.798%   $160.7392   $160.74   $160.75   $160.70  
  Purchase #4 $21.51   13.635%   $24.4429   $24.44   $24.45   $24.40  
  Purchase #5 $170.84   10.698%   $189.1165   $189.12   $189.10   $189.10  
  Purchase #6 $166.72   10.813%   $184.7474   $184.75   $184.75   $184.70  
  Purchase #7 $131.84   7.839%   $142.1749   $142.17   $142.15   $142.20  
  7 purchase totals = $964.22       $1,060.2165   $1,060.21   $1,060.20   $1,060.10