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	$50.59	11.731%	$56.5247	$56.52	$56.50	$56.50
Purchase #2	$221.89	4.438%	$231.7375	$231.74	$231.75	$231.70
Purchase #3	$207.92	13.415%	$235.8125	$235.81	$235.80	$235.80
Purchase #4	$56.39	5.407%	$59.439	$59.44	$59.45	$59.40
Purchase #5	$123.46	11.581%	$137.7579	$137.76	$137.75	$137.80
Purchase #6	$199.67	3.443%	$206.5446	$206.54	$206.55	$206.50
Purchase #7	$109.43	12.305%	$122.8954	$122.90	$122.90	$122.90
7 purchase totals =	$969.35		$1,050.7116	$1,050.71	$1,050.70	$1,050.60