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	$56.51	5.122%	$59.4044	$59.40	$59.40	$59.40
Purchase #2	$235.50	7.643%	$253.4993	$253.50	$253.50	$253.50
Purchase #3	$65.61	12.220%	$73.6275	$73.63	$73.65	$73.60
Purchase #4	$70.29	10.826%	$77.8996	$77.90	$77.90	$77.90
Purchase #5	$50.98	11.786%	$56.9885	$56.99	$57.00	$57.00
Purchase #6	$51.94	4.607%	$54.3329	$54.33	$54.35	$54.30
Purchase #7	$63.62	3.550%	$65.8785	$65.88	$65.90	$65.90
7 purchase totals =	$594.45		$641.6307	$641.63	$641.70	$641.60