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	$87.77	3.413%	$90.7656	$90.77	$90.75	$90.80
Purchase #2	$158.29	8.620%	$171.9346	$171.93	$171.95	$171.90
Purchase #3	$230.61	8.607%	$250.4586	$250.46	$250.45	$250.50
Purchase #4	$120.57	13.227%	$136.5178	$136.52	$136.50	$136.50
Purchase #5	$193.34	6.201%	$205.329	$205.33	$205.35	$205.30
Purchase #6	$104.83	11.731%	$117.1276	$117.13	$117.15	$117.10
Purchase #7	$189.54	3.153%	$195.5162	$195.52	$195.50	$195.50
7 purchase totals =	$1,084.95		$1,167.6494	$1,167.66	$1,167.65	$1,167.60