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 $223.48   8.136%   $241.6623   $241.66   $241.65   $241.70  
  Purchase #2 $222.33   11.305%   $247.4644   $247.46   $247.45   $247.50  
  Purchase #3 $156.71   12.461%   $176.2376   $176.24   $176.25   $176.20  
  Purchase #4 $20.58   11.576%   $22.9623   $22.96   $22.95   $23.00  
  Purchase #5 $218.77   13.839%   $249.0456   $249.05   $249.05   $249.00  
  Purchase #6 $131.63   7.599%   $141.6326   $141.63   $141.65   $141.60  
  Purchase #7 $180.29   10.355%   $198.959   $198.96   $198.95   $199.00  
  7 purchase totals = $1,153.79       $1,277.9638   $1,277.96   $1,277.95   $1,278.00