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	$45.90	11.200%	$51.0408	$51.04	$51.05	$51.00
Purchase #2	$89.50	12.158%	$100.3814	$100.38	$100.40	$100.40
Purchase #3	$139.73	8.703%	$151.8907	$151.89	$151.90	$151.90
Purchase #4	$37.88	11.436%	$42.212	$42.21	$42.20	$42.20
Purchase #5	$119.91	6.171%	$127.3096	$127.31	$127.30	$127.30
Purchase #6	$112.63	13.465%	$127.7956	$127.80	$127.80	$127.80
Purchase #7	$132.71	12.872%	$149.7924	$149.79	$149.80	$149.80
7 purchase totals =	$678.26		$750.4225	$750.42	$750.45	$750.40