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 $213.36   10.119%   $234.9499   $234.95   $234.95   $234.90  
  Purchase #2 $160.83   13.248%   $182.1368   $182.14   $182.15   $182.10  
  Purchase #3 $237.83   9.109%   $259.4939   $259.49   $259.50   $259.50  
  Purchase #4 $194.74   6.467%   $207.3338   $207.33   $207.35   $207.30  
  Purchase #5 $134.73   10.282%   $148.5829   $148.58   $148.60   $148.60  
  Purchase #6 $64.91   8.623%   $70.5072   $70.51   $70.50   $70.50  
  Purchase #7 $99.58   11.863%   $111.3932   $111.39   $111.40   $111.40  
  7 purchase totals = $1,105.98       $1,214.3977   $1,214.39   $1,214.45   $1,214.30