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 $76.63   9.216%   $83.6922   $83.69   $83.70   $83.70  
  Purchase #2 $164.54   10.703%   $182.1507   $182.15   $182.15   $182.20  
  Purchase #3 $183.44   6.388%   $195.1581   $195.16   $195.15   $195.20  
  Purchase #4 $25.98   5.722%   $27.4666   $27.47   $27.45   $27.50  
  Purchase #5 $244.79   9.134%   $267.1491   $267.15   $267.15   $267.10  
  Purchase #6 $213.55   6.832%   $228.1397   $228.14   $228.15   $228.10  
  Purchase #7 $177.27   4.253%   $184.8093   $184.81   $184.80   $184.80  
  7 purchase totals = $1,086.20       $1,168.5657   $1,168.57   $1,168.55   $1,168.60