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 $86.84   10.653%   $96.0911   $96.09   $96.10   $96.10  
  Purchase #2 $129.56   8.859%   $141.0377   $141.04   $141.05   $141.00  
  Purchase #3 $234.64   10.494%   $259.2631   $259.26   $259.25   $259.30  
  Purchase #4 $245.77   11.465%   $273.9475   $273.95   $273.95   $273.90  
  Purchase #5 $52.71   6.485%   $56.1282   $56.13   $56.15   $56.10  
  Purchase #6 $244.38   13.405%   $277.1391   $277.14   $277.15   $277.10  
  Purchase #7 $102.72   13.287%   $116.3684   $116.37   $116.35   $116.40  
  7 purchase totals = $1,096.62       $1,219.9751   $1,219.98   $1,220.00   $1,219.90