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	$159.26	8.674%	$173.0742	$173.07	$173.05	$173.10
Purchase #2	$112.69	9.525%	$123.4237	$123.42	$123.40	$123.40
Purchase #3	$184.39	8.474%	$200.0152	$200.02	$200.00	$200.00
Purchase #4	$25.96	10.637%	$28.7214	$28.72	$28.70	$28.70
Purchase #5	$117.34	8.135%	$126.8856	$126.89	$126.90	$126.90
Purchase #6	$179.42	11.644%	$200.3117	$200.31	$200.30	$200.30
Purchase #7	$57.43	6.229%	$61.0073	$61.01	$61.00	$61.00
7 purchase totals =	$836.49		$913.4391	$913.44	$913.35	$913.40