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 $118.39   4.863%   $124.1473   $124.15   $124.15   $124.10  
  Purchase #2 $188.59   7.726%   $203.1605   $203.16   $203.15   $203.20  
  Purchase #3 $52.58   8.546%   $57.0735   $57.07   $57.05   $57.10  
  Purchase #4 $225.69   4.574%   $236.0131   $236.01   $236.00   $236.00  
  Purchase #5 $30.49   5.195%   $32.074   $32.07   $32.05   $32.10  
  Purchase #6 $157.48   5.813%   $166.6343   $166.63   $166.65   $166.60  
  Purchase #7 $198.57   3.643%   $205.8039   $205.80   $205.80   $205.80  
  7 purchase totals = $971.79       $1,024.9066   $1,024.89   $1,024.85   $1,024.90