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	$20.41	5.471%	$21.5266	$21.53	$21.55	$21.50
Purchase #2	$80.77	5.557%	$85.2584	$85.26	$85.25	$85.30
Purchase #3	$103.88	4.647%	$108.7073	$108.71	$108.70	$108.70
Purchase #4	$167.69	12.792%	$189.1409	$189.14	$189.15	$189.10
Purchase #5	$63.31	12.750%	$71.382	$71.38	$71.40	$71.40
Purchase #6	$29.72	3.438%	$30.7418	$30.74	$30.75	$30.70
Purchase #7	$65.41	9.254%	$71.463	$71.46	$71.45	$71.50
7 purchase totals =	$531.19		$578.2200	$578.22	$578.25	$578.20