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 $89.26   7.198%   $95.6849   $95.68   $95.70   $95.70  
  Purchase #2 $75.61   5.159%   $79.5107   $79.51   $79.50   $79.50  
  Purchase #3 $37.72   6.523%   $40.1805   $40.18   $40.20   $40.20  
  Purchase #4 $220.73   11.151%   $245.3436   $245.34   $245.35   $245.30  
  Purchase #5 $174.38   8.785%   $189.6993   $189.70   $189.70   $189.70  
  Purchase #6 $246.55   8.680%   $267.9505   $267.95   $267.95   $268.00  
  Purchase #7 $7.84   7.501%   $8.4281   $8.43   $8.45   $8.40  
  7 purchase totals = $852.09       $926.7976   $926.79   $926.85   $926.80