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	$52.40	6.102%	$55.5974	$55.60	$55.60	$55.60
Purchase #2	$250.28	7.497%	$269.0435	$269.04	$269.05	$269.00
Purchase #3	$6.29	3.342%	$6.5002	$6.50	$6.50	$6.50
Purchase #4	$69.51	6.259%	$73.8606	$73.86	$73.85	$73.90
Purchase #5	$48.41	9.413%	$52.9668	$52.97	$52.95	$53.00
Purchase #6	$85.30	4.419%	$89.0694	$89.07	$89.05	$89.10
Purchase #7	$77.70	7.427%	$83.4708	$83.47	$83.45	$83.50
7 purchase totals =	$589.89		$630.5087	$630.51	$630.45	$630.60