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 $67.92   11.174%   $75.5094   $75.51   $75.50   $75.50  
  Purchase #2 $228.38   9.150%   $249.2768   $249.28   $249.30   $249.30  
  Purchase #3 $14.69   3.756%   $15.2418   $15.24   $15.25   $15.20  
  Purchase #4 $60.46   12.514%   $68.026   $68.03   $68.05   $68.00  
  Purchase #5 $104.72   13.140%   $118.4802   $118.48   $118.50   $118.50  
  Purchase #6 $174.32   8.561%   $189.2435   $189.24   $189.25   $189.20  
  Purchase #7 $181.80   5.159%   $191.1791   $191.18   $191.20   $191.20  
  7 purchase totals = $832.29       $906.9568   $906.96   $907.05   $906.90