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	$134.45	3.548%	$139.2203	$139.22	$139.20	$139.20
Purchase #2	$181.90	4.480%	$190.0491	$190.05	$190.05	$190.00
Purchase #3	$102.68	11.727%	$114.7213	$114.72	$114.70	$114.70
Purchase #4	$73.62	6.135%	$78.1366	$78.14	$78.15	$78.10
Purchase #5	$150.66	3.301%	$155.6333	$155.63	$155.65	$155.60
Purchase #6	$159.93	6.210%	$169.8617	$169.86	$169.85	$169.90
Purchase #7	$214.54	13.311%	$243.0974	$243.10	$243.10	$243.10
7 purchase totals =	$1,017.78		$1,090.7197	$1,090.72	$1,090.70	$1,090.60