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	$133.43	12.602%	$150.2448	$150.24	$150.25	$150.20
Purchase #2	$64.40	7.255%	$69.0722	$69.07	$69.05	$69.10
Purchase #3	$73.72	11.614%	$82.2818	$82.28	$82.30	$82.30
Purchase #4	$29.35	8.228%	$31.7649	$31.76	$31.75	$31.80
Purchase #5	$64.51	10.123%	$71.0403	$71.04	$71.05	$71.00
Purchase #6	$119.66	9.242%	$130.719	$130.72	$130.70	$130.70
Purchase #7	$37.74	12.400%	$42.4198	$42.42	$42.40	$42.40
7 purchase totals =	$522.81		$577.5428	$577.53	$577.50	$577.50