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 $220.39   9.761%   $241.9023   $241.90   $241.90   $241.90  
  Purchase #2 $206.35   10.410%   $227.831   $227.83   $227.85   $227.80  
  Purchase #3 $55.28   3.431%   $57.1767   $57.18   $57.20   $57.20  
  Purchase #4 $221.25   10.395%   $244.2489   $244.25   $244.25   $244.20  
  Purchase #5 $38.32   6.582%   $40.8422   $40.84   $40.85   $40.80  
  Purchase #6 $206.87   7.531%   $222.4494   $222.45   $222.45   $222.40  
  Purchase #7 $177.26   10.513%   $195.8953   $195.90   $195.90   $195.90  
  7 purchase totals = $1,125.72       $1,230.3458   $1,230.35   $1,230.40   $1,230.20