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	$18.50	4.427%	$19.319	$19.32	$19.30	$19.30
Purchase #2	$43.65	9.616%	$47.8474	$47.85	$47.85	$47.80
Purchase #3	$128.81	11.384%	$143.4737	$143.47	$143.45	$143.50
Purchase #4	$127.89	10.524%	$141.3491	$141.35	$141.35	$141.30
Purchase #5	$176.54	11.445%	$196.745	$196.75	$196.75	$196.70
Purchase #6	$10.76	6.753%	$11.4866	$11.49	$11.50	$11.50
Purchase #7	$94.34	3.359%	$97.5089	$97.51	$97.50	$97.50
7 purchase totals =	$600.49		$657.7297	$657.74	$657.70	$657.60