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 $161.58   13.644%   $183.626   $183.63   $183.65   $183.60  
  Purchase #2 $211.44   6.579%   $225.3506   $225.35   $225.35   $225.40  
  Purchase #3 $80.43   5.670%   $84.9904   $84.99   $85.00   $85.00  
  Purchase #4 $216.68   12.617%   $244.0185   $244.02   $244.00   $244.00  
  Purchase #5 $206.43   10.538%   $228.1836   $228.18   $228.20   $228.20  
  Purchase #6 $206.66   6.685%   $220.4752   $220.48   $220.50   $220.50  
  Purchase #7 $77.97   7.388%   $83.7304   $83.73   $83.75   $83.70  
  7 purchase totals = $1,161.19       $1,270.3747   $1,270.38   $1,270.45   $1,270.40