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 $206.80   9.304%   $226.0407   $226.04   $226.05   $226.00  
  Purchase #2 $141.78   5.313%   $149.3128   $149.31   $149.30   $149.30  
  Purchase #3 $56.66   4.784%   $59.3706   $59.37   $59.35   $59.40  
  Purchase #4 $76.86   9.153%   $83.895   $83.90   $83.90   $83.90  
  Purchase #5 $57.79   7.334%   $62.0283   $62.03   $62.05   $62.00  
  Purchase #6 $45.94   8.435%   $49.815   $49.82   $49.80   $49.80  
  Purchase #7 $86.49   5.353%   $91.1198   $91.12   $91.10   $91.10  
  7 purchase totals = $672.32       $721.5822   $721.59   $721.55   $721.50