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	$137.78	7.745%	$148.4511	$148.45	$148.45	$148.50
Purchase #2	$229.75	9.179%	$250.8388	$250.84	$250.85	$250.80
Purchase #3	$239.41	8.134%	$258.8836	$258.88	$258.90	$258.90
Purchase #4	$150.46	11.613%	$167.9329	$167.93	$167.95	$167.90
Purchase #5	$98.50	3.283%	$101.7338	$101.73	$101.75	$101.70
Purchase #6	$192.59	8.585%	$209.1239	$209.12	$209.10	$209.10
Purchase #7	$128.27	11.716%	$143.2981	$143.30	$143.30	$143.30
7 purchase totals =	$1,176.76		$1,280.2622	$1,280.25	$1,280.30	$1,280.20