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 $32.64   8.267%   $35.3383   $35.34   $35.35   $35.30  
  Purchase #2 $211.38   4.487%   $220.8646   $220.86   $220.85   $220.90  
  Purchase #3 $114.68   8.534%   $124.4668   $124.47   $124.45   $124.50  
  Purchase #4 $231.67   9.257%   $253.1157   $253.12   $253.10   $253.10  
  Purchase #5 $110.61   8.283%   $119.7718   $119.77   $119.75   $119.80  
  Purchase #6 $24.59   6.725%   $26.2437   $26.24   $26.25   $26.20  
  Purchase #7 $237.53   13.659%   $269.9742   $269.97   $269.95   $270.00  
  7 purchase totals = $963.10       $1,049.7751   $1,049.77   $1,049.70   $1,049.80