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	$236.65	6.217%	$251.3625	$251.36	$251.35	$251.40
Purchase #2	$162.40	4.412%	$169.5651	$169.57	$169.55	$169.60
Purchase #3	$94.75	6.482%	$100.8917	$100.89	$100.90	$100.90
Purchase #4	$90.98	10.831%	$100.834	$100.83	$100.85	$100.80
Purchase #5	$35.97	4.243%	$37.4962	$37.50	$37.50	$37.50
Purchase #6	$182.96	12.548%	$205.9178	$205.92	$205.90	$205.90
Purchase #7	$130.48	9.632%	$143.0478	$143.05	$143.05	$143.00
7 purchase totals =	$934.19		$1,009.1151	$1,009.12	$1,009.10	$1,009.10