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	$46.89	7.411%	$50.365	$50.37	$50.35	$50.40
Purchase #2	$131.25	4.430%	$137.0644	$137.06	$137.05	$137.10
Purchase #3	$207.84	12.466%	$233.7493	$233.75	$233.75	$233.70
Purchase #4	$78.77	13.378%	$89.3079	$89.31	$89.30	$89.30
Purchase #5	$146.61	8.621%	$159.2492	$159.25	$159.25	$159.20
Purchase #6	$126.37	11.832%	$141.3221	$141.32	$141.30	$141.30
Purchase #7	$180.67	11.717%	$201.8391	$201.84	$201.85	$201.80
7 purchase totals =	$918.40		$1,012.8970	$1,012.90	$1,012.85	$1,012.80