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	$84.81	6.498%	$90.321	$90.32	$90.30	$90.30
Purchase #2	$140.48	13.187%	$159.0051	$159.01	$159.00	$159.00
Purchase #3	$156.77	5.438%	$165.2952	$165.30	$165.30	$165.30
Purchase #4	$197.94	6.767%	$211.3346	$211.33	$211.35	$211.30
Purchase #5	$54.26	4.497%	$56.7001	$56.70	$56.70	$56.70
Purchase #6	$177.98	4.399%	$185.8093	$185.81	$185.80	$185.80
Purchase #7	$62.29	13.191%	$70.5067	$70.51	$70.50	$70.50
7 purchase totals =	$874.53		$938.9720	$938.98	$938.95	$938.90