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 $241.30   4.517%   $252.1995   $252.20   $252.20   $252.20  
  Purchase #2 $167.45   5.426%   $176.5358   $176.54   $176.55   $176.50  
  Purchase #3 $72.92   13.685%   $82.8991   $82.90   $82.90   $82.90  
  Purchase #4 $185.95   10.779%   $205.9936   $205.99   $206.00   $206.00  
  Purchase #5 $34.76   12.327%   $39.0449   $39.04   $39.05   $39.00  
  Purchase #6 $122.54   11.449%   $136.5696   $136.57   $136.55   $136.60  
  Purchase #7 $128.43   9.439%   $140.5525   $140.55   $140.55   $140.60  
  7 purchase totals = $953.35       $1,033.7950   $1,033.79   $1,033.80   $1,033.80