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 $11.51   4.603%   $12.0398   $12.04   $12.05   $12.00  
  Purchase #2 $91.87   4.817%   $96.2954   $96.30   $96.30   $96.30  
  Purchase #3 $69.73   11.496%   $77.7462   $77.75   $77.75   $77.70  
  Purchase #4 $89.34   12.545%   $100.5477   $100.55   $100.55   $100.50  
  Purchase #5 $183.64   3.474%   $190.0197   $190.02   $190.00   $190.00  
  Purchase #6 $227.94   4.614%   $238.4572   $238.46   $238.45   $238.50  
  Purchase #7 $95.35   13.216%   $107.9515   $107.95   $107.95   $108.00  
  7 purchase totals = $769.38       $823.0575   $823.07   $823.05   $823.00