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	$48.42	10.685%	$53.5937	$53.59	$53.60	$53.60
Purchase #2	$93.42	12.460%	$105.0601	$105.06	$105.05	$105.10
Purchase #3	$127.73	13.468%	$144.9327	$144.93	$144.95	$144.90
Purchase #4	$143.41	10.605%	$158.6186	$158.62	$158.60	$158.60
Purchase #5	$91.44	8.717%	$99.4108	$99.41	$99.40	$99.40
Purchase #6	$143.84	5.834%	$152.2316	$152.23	$152.25	$152.20
Purchase #7	$201.92	11.517%	$225.1751	$225.18	$225.20	$225.20
7 purchase totals =	$850.18		$939.0226	$939.02	$939.05	$939.00