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 $88.65   11.271%   $98.6417   $98.64   $98.65   $98.60  
  Purchase #2 $174.38   11.508%   $194.4477   $194.45   $194.45   $194.40  
  Purchase #3 $220.95   13.592%   $250.9815   $250.98   $251.00   $251.00  
  Purchase #4 $98.53   6.835%   $105.2645   $105.26   $105.25   $105.30  
  Purchase #5 $190.87   3.396%   $197.3519   $197.35   $197.35   $197.40  
  Purchase #6 $92.35   8.801%   $100.4777   $100.48   $100.50   $100.50  
  Purchase #7 $235.95   10.759%   $261.3359   $261.34   $261.35   $261.30  
  7 purchase totals = $1,101.68       $1,208.5009   $1,208.50   $1,208.55   $1,208.50