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 $58.28   4.313%   $60.7936   $60.79   $60.80   $60.80  
  Purchase #2 $48.72   11.631%   $54.3866   $54.39   $54.40   $54.40  
  Purchase #3 $249.53   11.798%   $278.9695   $278.97   $278.95   $279.00  
  Purchase #4 $196.25   4.762%   $205.5954   $205.60   $205.60   $205.60  
  Purchase #5 $90.53   3.858%   $94.0226   $94.02   $94.00   $94.00  
  Purchase #6 $243.99   8.355%   $264.3754   $264.38   $264.40   $264.40  
  Purchase #7 $180.25   13.819%   $205.1587   $205.16   $205.15   $205.20  
  7 purchase totals = $1,067.55       $1,163.3018   $1,163.31   $1,163.30   $1,163.40