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 $114.64   4.619%   $119.9352   $119.94   $119.95   $119.90  
  Purchase #2 $206.51   8.569%   $224.2058   $224.21   $224.20   $224.20  
  Purchase #3 $134.68   5.140%   $141.6026   $141.60   $141.60   $141.60  
  Purchase #4 $189.64   8.130%   $205.0577   $205.06   $205.05   $205.10  
  Purchase #5 $95.70   6.560%   $101.9779   $101.98   $102.00   $102.00  
  Purchase #6 $22.71   6.782%   $24.2502   $24.25   $24.25   $24.30  
  Purchase #7 $230.87   8.734%   $251.0342   $251.03   $251.05   $251.00  
  7 purchase totals = $994.75       $1,068.0636   $1,068.07   $1,068.10   $1,068.10