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 $95.79   7.532%   $103.0049   $103.00   $103.00   $103.00  
  Purchase #2 $242.63   9.697%   $266.1578   $266.16   $266.15   $266.20  
  Purchase #3 $199.45   10.269%   $219.9315   $219.93   $219.95   $219.90  
  Purchase #4 $231.27   5.869%   $244.8432   $244.84   $244.85   $244.80  
  Purchase #5 $50.35   11.758%   $56.2702   $56.27   $56.25   $56.30  
  Purchase #6 $101.53   10.526%   $112.217   $112.22   $112.20   $112.20  
  Purchase #7 $33.67   9.865%   $36.9915   $36.99   $37.00   $37.00  
  7 purchase totals = $954.69       $1,039.4161   $1,039.41   $1,039.40   $1,039.40