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 $41.28   10.517%   $45.6214   $45.62   $45.60   $45.60  
  Purchase #2 $221.83   8.686%   $241.0982   $241.10   $241.10   $241.10  
  Purchase #3 $19.87   3.804%   $20.6259   $20.63   $20.65   $20.60  
  Purchase #4 $238.87   11.678%   $266.7652   $266.77   $266.75   $266.80  
  Purchase #5 $188.25   13.196%   $213.0915   $213.09   $213.10   $213.10  
  Purchase #6 $106.79   12.294%   $119.9188   $119.92   $119.90   $119.90  
  Purchase #7 $135.46   10.176%   $149.2444   $149.24   $149.25   $149.20  
  7 purchase totals = $952.35       $1,056.3654   $1,056.37   $1,056.35   $1,056.30