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 $223.68   7.744%   $241.0018   $241.00   $241.00   $241.00  
  Purchase #2 $65.61   9.225%   $71.6625   $71.66   $71.65   $71.70  
  Purchase #3 $225.70   6.747%   $240.928   $240.93   $240.95   $240.90  
  Purchase #4 $88.76   8.486%   $96.2922   $96.29   $96.30   $96.30  
  Purchase #5 $103.28   5.313%   $108.7673   $108.77   $108.75   $108.80  
  Purchase #6 $118.51   10.228%   $130.6312   $130.63   $130.65   $130.60  
  Purchase #7 $66.57   5.117%   $69.9764   $69.98   $70.00   $70.00  
  7 purchase totals = $892.11       $959.2594   $959.26   $959.30   $959.30