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 $239.30   6.148%   $254.0122   $254.01   $254.00   $254.00  
  Purchase #2 $21.35   7.110%   $22.868   $22.87   $22.85   $22.90  
  Purchase #3 $44.95   11.733%   $50.224   $50.22   $50.20   $50.20  
  Purchase #4 $37.93   11.344%   $42.2328   $42.23   $42.25   $42.20  
  Purchase #5 $167.28   5.793%   $176.9705   $176.97   $176.95   $177.00  
  Purchase #6 $240.37   11.478%   $267.9597   $267.96   $267.95   $268.00  
  Purchase #7 $94.64   7.732%   $101.9576   $101.96   $101.95   $102.00  
  7 purchase totals = $845.82       $916.2248   $916.22   $916.15   $916.30