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	$84.31	5.598%	$89.0297	$89.03	$89.05	$89.00
Purchase #2	$190.28	6.428%	$202.5112	$202.51	$202.50	$202.50
Purchase #3	$36.43	11.764%	$40.7156	$40.72	$40.70	$40.70
Purchase #4	$140.25	4.405%	$146.428	$146.43	$146.45	$146.40
Purchase #5	$10.38	11.729%	$11.5975	$11.60	$11.60	$11.60
Purchase #6	$56.51	10.521%	$62.4554	$62.46	$62.45	$62.50
Purchase #7	$33.44	4.791%	$35.0421	$35.04	$35.05	$35.00
7 purchase totals =	$551.60		$587.7795	$587.79	$587.80	$587.70