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	$22.94	4.736%	$24.0264	$24.03	$24.05	$24.00
Purchase #2	$80.28	12.796%	$90.5526	$90.55	$90.55	$90.60
Purchase #3	$20.75	6.843%	$22.1699	$22.17	$22.15	$22.20
Purchase #4	$119.81	6.604%	$127.7223	$127.72	$127.70	$127.70
Purchase #5	$53.53	10.317%	$59.0527	$59.05	$59.05	$59.10
Purchase #6	$54.89	11.375%	$61.1337	$61.13	$61.15	$61.10
Purchase #7	$218.52	12.529%	$245.8984	$245.90	$245.90	$245.90
7 purchase totals =	$570.72		$630.5560	$630.55	$630.55	$630.60