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 $88.26   6.153%   $93.6906   $93.69   $93.70   $93.70  
  Purchase #2 $173.97   6.373%   $185.0571   $185.06   $185.05   $185.10  
  Purchase #3 $173.44   5.416%   $182.8335   $182.83   $182.85   $182.80  
  Purchase #4 $237.68   10.748%   $263.2258   $263.23   $263.25   $263.20  
  Purchase #5 $182.59   9.339%   $199.6421   $199.64   $199.65   $199.60  
  Purchase #6 $183.68   3.105%   $189.3833   $189.38   $189.40   $189.40  
  Purchase #7 $250.25   5.610%   $264.289   $264.29   $264.30   $264.30  
  7 purchase totals = $1,289.87       $1,378.1214   $1,378.12   $1,378.20   $1,378.10