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	$48.90	13.328%	$55.4174	$55.42	$55.40	$55.40
Purchase #2	$165.36	7.828%	$178.3044	$178.30	$178.30	$178.30
Purchase #3	$60.47	12.794%	$68.2065	$68.21	$68.20	$68.20
Purchase #4	$244.90	3.735%	$254.047	$254.05	$254.05	$254.00
Purchase #5	$93.30	7.222%	$100.0381	$100.04	$100.05	$100.00
Purchase #6	$80.49	11.156%	$89.4695	$89.47	$89.45	$89.50
Purchase #7	$230.91	13.419%	$261.8958	$261.90	$261.90	$261.90
7 purchase totals =	$924.33		$1,007.3787	$1,007.39	$1,007.35	$1,007.30