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 $198.63   13.113%   $224.6764   $224.68   $224.70   $224.70  
  Purchase #2 $200.61   10.589%   $221.8526   $221.85   $221.85   $221.90  
  Purchase #3 $19.70   11.181%   $21.9027   $21.90   $21.90   $21.90  
  Purchase #4 $225.71   9.216%   $246.5114   $246.51   $246.50   $246.50  
  Purchase #5 $51.31   5.212%   $53.9843   $53.98   $54.00   $54.00  
  Purchase #6 $101.48   12.521%   $114.1863   $114.19   $114.20   $114.20  
  Purchase #7 $167.61   6.119%   $177.8661   $177.87   $177.85   $177.90  
  7 purchase totals = $965.05       $1,060.9798   $1,060.98   $1,061.00   $1,061.10