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	$232.70	9.654%	$255.1649	$255.16	$255.15	$255.20
Purchase #2	$131.27	7.203%	$140.7254	$140.73	$140.75	$140.70
Purchase #3	$111.45	11.456%	$124.2177	$124.22	$124.20	$124.20
Purchase #4	$235.83	3.171%	$243.3082	$243.31	$243.30	$243.30
Purchase #5	$145.95	13.785%	$166.0692	$166.07	$166.05	$166.10
Purchase #6	$179.94	13.671%	$204.5396	$204.54	$204.55	$204.50
Purchase #7	$102.68	3.727%	$106.5069	$106.51	$106.50	$106.50
7 purchase totals =	$1,139.82		$1,240.5319	$1,240.54	$1,240.50	$1,240.50