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 $226.41   6.702%   $241.584   $241.58   $241.60   $241.60  
  Purchase #2 $13.42   5.269%   $14.1271   $14.13   $14.15   $14.10  
  Purchase #3 $218.34   8.162%   $236.1609   $236.16   $236.15   $236.20  
  Purchase #4 $32.55   9.139%   $35.5247   $35.52   $35.50   $35.50  
  Purchase #5 $80.62   3.562%   $83.4917   $83.49   $83.50   $83.50  
  Purchase #6 $167.25   12.422%   $188.0258   $188.03   $188.05   $188.00  
  Purchase #7 $147.29   5.664%   $155.6325   $155.63   $155.65   $155.60  
  7 purchase totals = $885.88       $954.5467   $954.54   $954.60   $954.50