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	$66.63	10.670%	$73.7394	$73.74	$73.75	$73.70
Purchase #2	$89.61	12.829%	$101.1061	$101.11	$101.10	$101.10
Purchase #3	$56.89	4.289%	$59.33	$59.33	$59.35	$59.30
Purchase #4	$57.62	13.140%	$65.1913	$65.19	$65.20	$65.20
Purchase #5	$239.61	7.165%	$256.7781	$256.78	$256.80	$256.80
Purchase #6	$185.56	8.140%	$200.6646	$200.66	$200.65	$200.70
Purchase #7	$52.97	11.133%	$58.8672	$58.87	$58.85	$58.90
7 purchase totals =	$748.89		$815.6767	$815.68	$815.70	$815.70