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	$135.50	5.754%	$143.2967	$143.30	$143.30	$143.30
Purchase #2	$173.36	5.851%	$183.5033	$183.50	$183.50	$183.50
Purchase #3	$134.92	4.460%	$140.9374	$140.94	$140.95	$140.90
Purchase #4	$145.58	11.663%	$162.559	$162.56	$162.55	$162.60
Purchase #5	$127.41	12.366%	$143.1655	$143.17	$143.15	$143.20
Purchase #6	$97.33	7.203%	$104.3407	$104.34	$104.35	$104.30
Purchase #7	$242.29	6.680%	$258.475	$258.48	$258.50	$258.50
7 purchase totals =	$1,056.39		$1,136.2776	$1,136.29	$1,136.30	$1,136.30