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 $83.87   13.400%   $95.1086   $95.11   $95.10   $95.10  
  Purchase #2 $61.88   10.318%   $68.2648   $68.26   $68.25   $68.30  
  Purchase #3 $206.95   11.808%   $231.3867   $231.39   $231.40   $231.40  
  Purchase #4 $159.35   10.413%   $175.9431   $175.94   $175.95   $175.90  
  Purchase #5 $19.43   13.474%   $22.048   $22.05   $22.05   $22.00  
  Purchase #6 $149.38   3.522%   $154.6412   $154.64   $154.65   $154.60  
  Purchase #7 $69.44   10.402%   $76.6631   $76.66   $76.65   $76.70  
  7 purchase totals = $750.30       $824.0555   $824.05   $824.05   $824.00