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 $209.57   4.445%   $218.8854   $218.89   $218.90   $218.90  
  Purchase #2 $63.51   4.871%   $66.6036   $66.60   $66.60   $66.60  
  Purchase #3 $130.90   4.651%   $136.9882   $136.99   $137.00   $137.00  
  Purchase #4 $183.69   6.319%   $195.2974   $195.30   $195.30   $195.30  
  Purchase #5 $192.93   11.246%   $214.6269   $214.63   $214.65   $214.60  
  Purchase #6 $41.90   5.329%   $44.1329   $44.13   $44.15   $44.10  
  Purchase #7 $96.56   5.847%   $102.2059   $102.21   $102.20   $102.20  
  7 purchase totals = $919.06       $978.7403   $978.75   $978.80   $978.70