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	$61.39	6.627%	$65.4583	$65.46	$65.45	$65.50
Purchase #2	$155.29	11.614%	$173.3254	$173.33	$173.35	$173.30
Purchase #3	$242.90	5.354%	$255.9049	$255.90	$255.90	$255.90
Purchase #4	$13.86	12.760%	$15.6285	$15.63	$15.65	$15.60
Purchase #5	$32.52	8.251%	$35.2032	$35.20	$35.20	$35.20
Purchase #6	$109.68	10.137%	$120.7983	$120.80	$120.80	$120.80
Purchase #7	$102.25	12.360%	$114.8881	$114.89	$114.90	$114.90
7 purchase totals =	$717.89		$781.2067	$781.21	$781.25	$781.20