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 $51.39   4.846%   $53.8804   $53.88   $53.90   $53.90  
  Purchase #2 $93.25   3.643%   $96.6471   $96.65   $96.65   $96.60  
  Purchase #3 $86.33   7.182%   $92.5302   $92.53   $92.55   $92.50  
  Purchase #4 $214.93   13.604%   $244.1691   $244.17   $244.15   $244.20  
  Purchase #5 $200.60   13.771%   $228.2246   $228.22   $228.20   $228.20  
  Purchase #6 $78.87   9.454%   $86.3264   $86.33   $86.35   $86.30  
  Purchase #7 $192.60   9.179%   $210.2788   $210.28   $210.30   $210.30  
  7 purchase totals = $917.97       $1,012.0566   $1,012.06   $1,012.10   $1,012.00