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	$146.56	3.368%	$151.4961	$151.50	$151.50	$151.50
Purchase #2	$13.80	5.474%	$14.5554	$14.56	$14.55	$14.60
Purchase #3	$223.38	12.419%	$251.1216	$251.12	$251.10	$251.10
Purchase #4	$38.75	8.126%	$41.8988	$41.90	$41.90	$41.90
Purchase #5	$236.79	10.391%	$261.3948	$261.39	$261.40	$261.40
Purchase #6	$165.93	13.603%	$188.5015	$188.50	$188.50	$188.50
Purchase #7	$89.66	10.776%	$99.3218	$99.32	$99.30	$99.30
7 purchase totals =	$914.87		$1,008.2900	$1,008.29	$1,008.25	$1,008.30