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 $201.26   9.206%   $219.788   $219.79   $219.80   $219.80  
  Purchase #2 $145.65   10.321%   $160.6825   $160.68   $160.70   $160.70  
  Purchase #3 $55.86   13.475%   $63.3871   $63.39   $63.40   $63.40  
  Purchase #4 $89.27   3.789%   $92.6524   $92.65   $92.65   $92.70  
  Purchase #5 $214.66   13.187%   $242.9672   $242.97   $242.95   $243.00  
  Purchase #6 $116.63   11.648%   $130.2151   $130.22   $130.20   $130.20  
  Purchase #7 $42.60   7.166%   $45.6527   $45.65   $45.65   $45.70  
  7 purchase totals = $865.93       $955.3450   $955.35   $955.35   $955.50