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	$148.39	12.129%	$166.3882	$166.39	$166.40	$166.40
Purchase #2	$26.28	5.599%	$27.7514	$27.75	$27.75	$27.80
Purchase #3	$246.45	11.821%	$275.5829	$275.58	$275.60	$275.60
Purchase #4	$104.95	5.249%	$110.4588	$110.46	$110.45	$110.50
Purchase #5	$150.53	4.111%	$156.7183	$156.72	$156.70	$156.70
Purchase #6	$243.77	3.333%	$251.8949	$251.89	$251.90	$251.90
Purchase #7	$61.60	6.788%	$65.7814	$65.78	$65.80	$65.80
7 purchase totals =	$981.97		$1,054.5759	$1,054.57	$1,054.60	$1,054.70