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	$104.27	12.767%	$117.5822	$117.58	$117.60	$117.60
Purchase #2	$165.26	6.819%	$176.5291	$176.53	$176.55	$176.50
Purchase #3	$105.90	3.281%	$109.3746	$109.37	$109.35	$109.40
Purchase #4	$241.27	8.362%	$261.445	$261.45	$261.45	$261.40
Purchase #5	$82.74	11.105%	$91.9283	$91.93	$91.95	$91.90
Purchase #6	$67.80	10.811%	$75.1299	$75.13	$75.15	$75.10
Purchase #7	$250.41	7.388%	$268.9103	$268.91	$268.90	$268.90
7 purchase totals =	$1,017.65		$1,100.8994	$1,100.90	$1,100.95	$1,100.80