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 $23.46   8.661%   $25.4919   $25.49   $25.50   $25.50  
  Purchase #2 $41.82   7.822%   $45.0912   $45.09   $45.10   $45.10  
  Purchase #3 $45.75   6.837%   $48.8779   $48.88   $48.90   $48.90  
  Purchase #4 $232.27   3.742%   $240.9615   $240.96   $240.95   $241.00  
  Purchase #5 $195.61   8.580%   $212.3933   $212.39   $212.40   $212.40  
  Purchase #6 $65.43   11.647%   $73.0506   $73.05   $73.05   $73.10  
  Purchase #7 $189.86   11.872%   $212.4002   $212.40   $212.40   $212.40  
  7 purchase totals = $794.20       $858.2666   $858.26   $858.30   $858.40