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	$100.37	4.176%	$104.5615	$104.56	$104.55	$104.60
Purchase #2	$83.32	5.740%	$88.1026	$88.10	$88.10	$88.10
Purchase #3	$225.26	9.335%	$246.288	$246.29	$246.30	$246.30
Purchase #4	$81.48	13.546%	$92.5173	$92.52	$92.50	$92.50
Purchase #5	$168.63	13.727%	$191.7778	$191.78	$191.80	$191.80
Purchase #6	$40.69	10.704%	$45.0455	$45.05	$45.05	$45.00
Purchase #7	$74.88	5.369%	$78.9003	$78.90	$78.90	$78.90
7 purchase totals =	$774.63		$847.1930	$847.20	$847.20	$847.20