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	$18.41	10.309%	$20.3079	$20.31	$20.30	$20.30
Purchase #2	$92.58	13.291%	$104.8848	$104.88	$104.90	$104.90
Purchase #3	$72.89	5.852%	$77.1555	$77.16	$77.15	$77.20
Purchase #4	$175.48	4.570%	$183.4994	$183.50	$183.50	$183.50
Purchase #5	$82.31	9.460%	$90.0965	$90.10	$90.10	$90.10
Purchase #6	$169.71	8.725%	$184.5172	$184.52	$184.50	$184.50
Purchase #7	$179.33	10.223%	$197.6629	$197.66	$197.65	$197.70
7 purchase totals =	$790.71		$858.1242	$858.13	$858.10	$858.20