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	$144.37	10.750%	$159.8898	$159.89	$159.90	$159.90
Purchase #2	$111.66	3.363%	$115.4151	$115.42	$115.40	$115.40
Purchase #3	$82.88	11.446%	$92.3664	$92.37	$92.35	$92.40
Purchase #4	$100.49	9.361%	$109.8969	$109.90	$109.90	$109.90
Purchase #5	$149.90	4.411%	$156.5121	$156.51	$156.50	$156.50
Purchase #6	$23.38	7.535%	$25.1417	$25.14	$25.15	$25.10
Purchase #7	$130.69	7.554%	$140.5623	$140.56	$140.55	$140.60
7 purchase totals =	$743.37		$799.7843	$799.79	$799.75	$799.80