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	$22.38	7.760%	$24.1167	$24.12	$24.10	$24.10
Purchase #2	$53.61	5.426%	$56.5189	$56.52	$56.50	$56.50
Purchase #3	$189.66	11.400%	$211.2812	$211.28	$211.30	$211.30
Purchase #4	$146.84	8.501%	$159.3229	$159.32	$159.30	$159.30
Purchase #5	$96.55	4.417%	$100.8146	$100.81	$100.80	$100.80
Purchase #6	$30.75	4.317%	$32.0775	$32.08	$32.10	$32.10
Purchase #7	$81.52	4.540%	$85.221	$85.22	$85.20	$85.20
7 purchase totals =	$621.31		$669.3528	$669.35	$669.30	$669.30