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	$189.95	10.840%	$210.5406	$210.54	$210.55	$210.50
Purchase #2	$210.41	6.166%	$223.3839	$223.38	$223.40	$223.40
Purchase #3	$242.28	13.845%	$275.8237	$275.82	$275.80	$275.80
Purchase #4	$140.90	11.414%	$156.9823	$156.98	$157.00	$157.00
Purchase #5	$93.72	6.778%	$100.0723	$100.07	$100.05	$100.10
Purchase #6	$65.71	4.747%	$68.8293	$68.83	$68.85	$68.80
Purchase #7	$50.29	13.615%	$57.137	$57.14	$57.15	$57.10
7 purchase totals =	$993.26		$1,092.7691	$1,092.76	$1,092.80	$1,092.70