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	$240.78	3.279%	$248.6752	$248.68	$248.70	$248.70
Purchase #2	$78.56	12.818%	$88.6298	$88.63	$88.65	$88.60
Purchase #3	$99.96	4.247%	$104.2053	$104.21	$104.20	$104.20
Purchase #4	$89.80	10.499%	$99.2281	$99.23	$99.25	$99.20
Purchase #5	$45.88	10.341%	$50.6245	$50.62	$50.60	$50.60
Purchase #6	$71.26	7.198%	$76.3893	$76.39	$76.40	$76.40
Purchase #7	$210.77	4.146%	$219.5085	$219.51	$219.50	$219.50
7 purchase totals =	$837.01		$887.2607	$887.27	$887.30	$887.20