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 $107.53   10.822%   $119.1669   $119.17   $119.15   $119.20  
  Purchase #2 $62.97   6.119%   $66.8231   $66.82   $66.80   $66.80  
  Purchase #3 $103.26   5.183%   $108.612   $108.61   $108.60   $108.60  
  Purchase #4 $164.84   7.549%   $177.2838   $177.28   $177.30   $177.30  
  Purchase #5 $139.97   9.462%   $153.214   $153.21   $153.20   $153.20  
  Purchase #6 $179.98   10.297%   $198.5125   $198.51   $198.50   $198.50  
  Purchase #7 $122.69   11.689%   $137.0312   $137.03   $137.05   $137.00  
  7 purchase totals = $881.24       $960.6435   $960.63   $960.60   $960.60