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	$98.63	6.865%	$105.4009	$105.40	$105.40	$105.40
Purchase #2	$127.69	11.118%	$141.8866	$141.89	$141.90	$141.90
Purchase #3	$210.43	11.746%	$235.1471	$235.15	$235.15	$235.10
Purchase #4	$89.68	10.526%	$99.1197	$99.12	$99.10	$99.10
Purchase #5	$66.54	10.386%	$73.4508	$73.45	$73.45	$73.50
Purchase #6	$178.52	4.828%	$187.1389	$187.14	$187.15	$187.10
Purchase #7	$83.46	6.245%	$88.6721	$88.67	$88.65	$88.70
7 purchase totals =	$854.95		$930.8161	$930.82	$930.80	$930.80