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	$155.38	12.237%	$174.3939	$174.39	$174.40	$174.40
Purchase #2	$89.49	11.729%	$99.9863	$99.99	$100.00	$100.00
Purchase #3	$196.92	6.472%	$209.6647	$209.66	$209.65	$209.70
Purchase #4	$34.35	3.157%	$35.4344	$35.43	$35.45	$35.40
Purchase #5	$87.77	13.236%	$99.3872	$99.39	$99.40	$99.40
Purchase #6	$18.89	11.154%	$20.997	$21.00	$21.00	$21.00
Purchase #7	$28.63	13.211%	$32.4123	$32.41	$32.40	$32.40
7 purchase totals =	$611.43		$672.2758	$672.27	$672.30	$672.30