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	$28.43	9.851%	$31.2306	$31.23	$31.25	$31.20
Purchase #2	$56.64	9.303%	$61.9092	$61.91	$61.90	$61.90
Purchase #3	$50.33	7.536%	$54.1229	$54.12	$54.10	$54.10
Purchase #4	$13.29	13.127%	$15.0346	$15.03	$15.05	$15.00
Purchase #5	$208.34	6.465%	$221.8092	$221.81	$221.80	$221.80
Purchase #6	$26.41	11.829%	$29.534	$29.53	$29.55	$29.50
Purchase #7	$61.39	13.510%	$69.6838	$69.68	$69.70	$69.70
7 purchase totals =	$444.83		$483.3243	$483.31	$483.35	$483.20