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	$46.48	13.417%	$52.7162	$52.72	$52.70	$52.70
Purchase #2	$155.75	9.528%	$170.5899	$170.59	$170.60	$170.60
Purchase #3	$233.69	4.311%	$243.7644	$243.76	$243.75	$243.80
Purchase #4	$59.58	3.276%	$61.5318	$61.53	$61.55	$61.50
Purchase #5	$246.76	3.356%	$255.0413	$255.04	$255.05	$255.00
Purchase #6	$209.84	10.840%	$232.5867	$232.59	$232.60	$232.60
Purchase #7	$123.60	3.221%	$127.5812	$127.58	$127.60	$127.60
7 purchase totals =	$1,075.70		$1,143.8115	$1,143.81	$1,143.85	$1,143.80