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 $90.76   11.529%   $101.2237   $101.22   $101.20   $101.20  
  Purchase #2 $213.90   12.484%   $240.6033   $240.60   $240.60   $240.60  
  Purchase #3 $37.51   7.644%   $40.3773   $40.38   $40.40   $40.40  
  Purchase #4 $144.70   4.593%   $151.3461   $151.35   $151.35   $151.30  
  Purchase #5 $233.92   9.666%   $256.5307   $256.53   $256.55   $256.50  
  Purchase #6 $167.30   6.246%   $177.7496   $177.75   $177.75   $177.70  
  Purchase #7 $67.61   12.445%   $76.0241   $76.02   $76.00   $76.00  
  7 purchase totals = $955.70       $1,043.8548   $1,043.85   $1,043.85   $1,043.70