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	$234.53	9.650%	$257.1621	$257.16	$257.15	$257.20
Purchase #2	$6.40	12.860%	$7.223	$7.22	$7.20	$7.20
Purchase #3	$74.25	6.207%	$78.8587	$78.86	$78.85	$78.90
Purchase #4	$55.30	10.269%	$60.9788	$60.98	$61.00	$61.00
Purchase #5	$31.58	11.555%	$35.2291	$35.23	$35.25	$35.20
Purchase #6	$241.66	13.317%	$273.8419	$273.84	$273.85	$273.80
Purchase #7	$33.80	4.508%	$35.3237	$35.32	$35.30	$35.30
7 purchase totals =	$677.52		$748.6173	$748.61	$748.60	$748.60