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	$70.35	11.429%	$78.3903	$78.39	$78.40	$78.40
Purchase #2	$82.58	7.575%	$88.8354	$88.84	$88.85	$88.80
Purchase #3	$189.60	4.606%	$198.333	$198.33	$198.35	$198.30
Purchase #4	$124.89	13.474%	$141.7177	$141.72	$141.70	$141.70
Purchase #5	$42.82	12.782%	$48.2933	$48.29	$48.30	$48.30
Purchase #6	$217.32	12.133%	$243.6874	$243.69	$243.70	$243.70
Purchase #7	$77.33	7.660%	$83.2535	$83.25	$83.25	$83.30
7 purchase totals =	$804.89		$882.5106	$882.51	$882.55	$882.50