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 $228.76   13.323%   $259.2377   $259.24   $259.25   $259.20  
  Purchase #2 $24.70   6.109%   $26.2089   $26.21   $26.20   $26.20  
  Purchase #3 $72.29   6.460%   $76.9599   $76.96   $76.95   $77.00  
  Purchase #4 $35.34   7.381%   $37.9484   $37.95   $37.95   $37.90  
  Purchase #5 $86.86   9.709%   $95.2932   $95.29   $95.30   $95.30  
  Purchase #6 $149.47   13.697%   $169.9429   $169.94   $169.95   $169.90  
  Purchase #7 $216.65   12.244%   $243.1766   $243.18   $243.20   $243.20  
  7 purchase totals = $814.07       $908.7676   $908.77   $908.80   $908.70