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 $88.43   4.268%   $92.2042   $92.20   $92.20   $92.20  
  Purchase #2 $189.50   9.177%   $206.8904   $206.89   $206.90   $206.90  
  Purchase #3 $179.91   5.206%   $189.2761   $189.28   $189.30   $189.30  
  Purchase #4 $248.98   13.311%   $282.1217   $282.12   $282.10   $282.10  
  Purchase #5 $53.54   13.200%   $60.6073   $60.61   $60.60   $60.60  
  Purchase #6 $205.25   3.614%   $212.6677   $212.67   $212.65   $212.70  
  Purchase #7 $158.79   8.624%   $172.484   $172.48   $172.50   $172.50  
  7 purchase totals = $1,124.40       $1,216.2514   $1,216.25   $1,216.25   $1,216.30