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	$87.57	3.336%	$90.4913	$90.49	$90.50	$90.50
Purchase #2	$217.40	8.747%	$236.416	$236.42	$236.40	$236.40
Purchase #3	$37.48	8.688%	$40.7363	$40.74	$40.75	$40.70
Purchase #4	$200.70	10.165%	$221.1012	$221.10	$221.10	$221.10
Purchase #5	$174.41	9.444%	$190.8813	$190.88	$190.90	$190.90
Purchase #6	$220.32	10.771%	$244.0507	$244.05	$244.05	$244.10
Purchase #7	$143.45	9.106%	$156.5126	$156.51	$156.50	$156.50
7 purchase totals =	$1,081.33		$1,180.1894	$1,180.19	$1,180.20	$1,180.20