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	$172.34	12.267%	$193.4809	$193.48	$193.50	$193.50
Purchase #2	$226.91	5.792%	$240.0526	$240.05	$240.05	$240.10
Purchase #3	$105.85	5.706%	$111.8898	$111.89	$111.90	$111.90
Purchase #4	$201.55	13.368%	$228.4932	$228.49	$228.50	$228.50
Purchase #5	$131.86	9.594%	$144.5106	$144.51	$144.50	$144.50
Purchase #6	$13.46	5.657%	$14.2214	$14.22	$14.20	$14.20
Purchase #7	$56.80	8.873%	$61.8399	$61.84	$61.85	$61.80
7 purchase totals =	$908.77		$994.4884	$994.48	$994.50	$994.50