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 $65.63   11.565%   $73.2201   $73.22   $73.20   $73.20  
  Purchase #2 $194.27   6.244%   $206.4002   $206.40   $206.40   $206.40  
  Purchase #3 $166.81   5.773%   $176.4399   $176.44   $176.45   $176.40  
  Purchase #4 $214.49   13.425%   $243.2853   $243.29   $243.30   $243.30  
  Purchase #5 $11.96   11.364%   $13.3191   $13.32   $13.30   $13.30  
  Purchase #6 $38.65   3.819%   $40.126   $40.13   $40.15   $40.10  
  Purchase #7 $138.37   10.241%   $152.5405   $152.54   $152.55   $152.50  
  7 purchase totals = $830.18       $905.3311   $905.34   $905.35   $905.20