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	$50.30	10.673%	$55.6685	$55.67	$55.65	$55.70
Purchase #2	$235.73	7.545%	$253.5158	$253.52	$253.50	$253.50
Purchase #3	$99.63	10.648%	$110.2386	$110.24	$110.25	$110.20
Purchase #4	$55.85	10.109%	$61.4959	$61.50	$61.50	$61.50
Purchase #5	$39.38	10.846%	$43.6512	$43.65	$43.65	$43.70
Purchase #6	$221.91	7.304%	$238.1183	$238.12	$238.10	$238.10
Purchase #7	$219.79	7.297%	$235.8281	$235.83	$235.85	$235.80
7 purchase totals =	$922.59		$998.5164	$998.53	$998.50	$998.50