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	$139.29	12.363%	$156.5104	$156.51	$156.50	$156.50
Purchase #2	$102.78	11.352%	$114.4476	$114.45	$114.45	$114.40
Purchase #3	$128.59	10.227%	$141.7409	$141.74	$141.75	$141.70
Purchase #4	$146.74	6.257%	$155.9215	$155.92	$155.90	$155.90
Purchase #5	$185.53	13.795%	$211.1239	$211.12	$211.10	$211.10
Purchase #6	$123.96	5.544%	$130.8323	$130.83	$130.85	$130.80
Purchase #7	$136.39	11.369%	$151.8962	$151.90	$151.90	$151.90
7 purchase totals =	$963.28		$1,062.4728	$1,062.47	$1,062.45	$1,062.30