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 $191.81   6.484%   $204.247   $204.25   $204.25   $204.20  
  Purchase #2 $33.36   12.871%   $37.6538   $37.65   $37.65   $37.70  
  Purchase #3 $170.68   8.738%   $185.594   $185.59   $185.60   $185.60  
  Purchase #4 $135.98   7.480%   $146.1513   $146.15   $146.15   $146.20  
  Purchase #5 $169.29   13.708%   $192.4963   $192.50   $192.50   $192.50  
  Purchase #6 $78.70   12.659%   $88.6626   $88.66   $88.65   $88.70  
  Purchase #7 $184.96   10.745%   $204.834   $204.83   $204.85   $204.80  
  7 purchase totals = $964.78       $1,059.6390   $1,059.63   $1,059.65   $1,059.70