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 $176.68   4.120%   $183.9592   $183.96   $183.95   $184.00  
  Purchase #2 $206.38   10.156%   $227.34   $227.34   $227.35   $227.30  
  Purchase #3 $216.57   4.171%   $225.6031   $225.60   $225.60   $225.60  
  Purchase #4 $124.55   3.548%   $128.969   $128.97   $128.95   $129.00  
  Purchase #5 $214.54   6.298%   $228.0517   $228.05   $228.05   $228.10  
  Purchase #6 $175.61   5.672%   $185.5706   $185.57   $185.55   $185.60  
  Purchase #7 $146.72   11.331%   $163.3448   $163.34   $163.35   $163.30  
  7 purchase totals = $1,261.05       $1,342.8384   $1,342.83   $1,342.80   $1,342.90