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 $69.82   4.711%   $73.1092   $73.11   $73.10   $73.10  
  Purchase #2 $62.40   6.353%   $66.3643   $66.36   $66.35   $66.40  
  Purchase #3 $125.61   9.486%   $137.5254   $137.53   $137.55   $137.50  
  Purchase #4 $230.40   10.442%   $254.4584   $254.46   $254.45   $254.50  
  Purchase #5 $218.38   4.110%   $227.3554   $227.36   $227.35   $227.40  
  Purchase #6 $179.62   13.708%   $204.2423   $204.24   $204.25   $204.20  
  Purchase #7 $89.40   9.746%   $98.1129   $98.11   $98.10   $98.10  
  7 purchase totals = $975.63       $1,061.1679   $1,061.17   $1,061.15   $1,061.20