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 $189.57   3.158%   $195.5566   $195.56   $195.55   $195.60  
  Purchase #2 $114.63   4.578%   $119.8778   $119.88   $119.90   $119.90  
  Purchase #3 $9.58   7.544%   $10.3027   $10.30   $10.30   $10.30  
  Purchase #4 $193.61   8.872%   $210.7871   $210.79   $210.80   $210.80  
  Purchase #5 $184.33   4.384%   $192.411   $192.41   $192.40   $192.40  
  Purchase #6 $208.28   8.671%   $226.34   $226.34   $226.35   $226.30  
  Purchase #7 $83.85   11.637%   $93.6076   $93.61   $93.60   $93.60  
  7 purchase totals = $983.85       $1,048.8828   $1,048.89   $1,048.90   $1,048.90