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 $42.85   10.519%   $47.3574   $47.36   $47.35   $47.40  
  Purchase #2 $192.95   7.643%   $207.6972   $207.70   $207.70   $207.70  
  Purchase #3 $154.40   4.242%   $160.9496   $160.95   $160.95   $160.90  
  Purchase #4 $240.95   4.652%   $252.159   $252.16   $252.15   $252.20  
  Purchase #5 $105.96   8.619%   $115.0927   $115.09   $115.10   $115.10  
  Purchase #6 $102.32   7.331%   $109.8211   $109.82   $109.80   $109.80  
  Purchase #7 $150.38   8.120%   $162.5909   $162.59   $162.60   $162.60  
  7 purchase totals = $989.81       $1,055.6679   $1,055.67   $1,055.65   $1,055.70