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	$250.47	6.215%	$266.0367	$266.04	$266.05	$266.00
Purchase #2	$57.56	3.103%	$59.3461	$59.35	$59.35	$59.30
Purchase #3	$229.48	6.249%	$243.8202	$243.82	$243.80	$243.80
Purchase #4	$240.72	11.205%	$267.6927	$267.69	$267.70	$267.70
Purchase #5	$166.52	3.801%	$172.8494	$172.85	$172.85	$172.80
Purchase #6	$48.53	11.323%	$54.0251	$54.03	$54.05	$54.00
Purchase #7	$56.86	5.700%	$60.101	$60.10	$60.10	$60.10
7 purchase totals =	$1,050.14		$1,123.8712	$1,123.88	$1,123.90	$1,123.70