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	$124.85	7.817%	$134.6095	$134.61	$134.60	$134.60
Purchase #2	$156.52	6.371%	$166.4919	$166.49	$166.50	$166.50
Purchase #3	$136.41	11.234%	$151.7343	$151.73	$151.75	$151.70
Purchase #4	$99.57	5.764%	$105.3092	$105.31	$105.30	$105.30
Purchase #5	$123.30	7.777%	$132.889	$132.89	$132.90	$132.90
Purchase #6	$61.67	4.117%	$64.209	$64.21	$64.20	$64.20
Purchase #7	$236.38	5.128%	$248.5016	$248.50	$248.50	$248.50
7 purchase totals =	$938.70		$1,003.7445	$1,003.74	$1,003.75	$1,003.70