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 $62.30   6.179%   $66.1495   $66.15   $66.15   $66.10  
  Purchase #2 $216.79   5.139%   $227.9308   $227.93   $227.95   $227.90  
  Purchase #3 $42.27   7.294%   $45.3532   $45.35   $45.35   $45.40  
  Purchase #4 $140.84   10.774%   $156.0141   $156.01   $156.00   $156.00  
  Purchase #5 $74.67   9.251%   $81.5777   $81.58   $81.60   $81.60  
  Purchase #6 $198.37   5.305%   $208.8935   $208.89   $208.90   $208.90  
  Purchase #7 $18.71   8.203%   $20.2448   $20.24   $20.25   $20.20  
  7 purchase totals = $753.95       $806.1636   $806.15   $806.20   $806.10