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 $221.84   11.308%   $246.9257   $246.93   $246.95   $246.90  
  Purchase #2 $114.48   4.277%   $119.3763   $119.38   $119.40   $119.40  
  Purchase #3 $177.43   12.652%   $199.8784   $199.88   $199.90   $199.90  
  Purchase #4 $34.86   3.746%   $36.1659   $36.17   $36.15   $36.20  
  Purchase #5 $178.77   10.317%   $197.2137   $197.21   $197.20   $197.20  
  Purchase #6 $58.25   12.416%   $65.4823   $65.48   $65.50   $65.50  
  Purchase #7 $174.32   7.397%   $187.2145   $187.21   $187.20   $187.20  
  7 purchase totals = $959.95       $1,052.2568   $1,052.26   $1,052.30   $1,052.30