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 $128.81   4.502%   $134.609   $134.61   $134.60   $134.60  
  Purchase #2 $33.44   4.156%   $34.8298   $34.83   $34.85   $34.80  
  Purchase #3 $247.61   9.689%   $271.6009   $271.60   $271.60   $271.60  
  Purchase #4 $216.94   10.582%   $239.8966   $239.90   $239.90   $239.90  
  Purchase #5 $169.25   10.428%   $186.8994   $186.90   $186.90   $186.90  
  Purchase #6 $183.34   5.500%   $193.4237   $193.42   $193.40   $193.40  
  Purchase #7 $234.28   4.222%   $244.1713   $244.17   $244.15   $244.20  
  7 purchase totals = $1,213.67       $1,305.4307   $1,305.43   $1,305.40   $1,305.40