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	$243.52	8.632%	$264.5406	$264.54	$264.55	$264.50
Purchase #2	$72.76	10.490%	$80.3925	$80.39	$80.40	$80.40
Purchase #3	$39.64	8.514%	$43.0149	$43.01	$43.00	$43.00
Purchase #4	$38.33	4.369%	$40.0046	$40.00	$40.00	$40.00
Purchase #5	$247.43	7.714%	$266.5168	$266.52	$266.50	$266.50
Purchase #6	$227.26	3.559%	$235.3482	$235.35	$235.35	$235.30
Purchase #7	$11.43	7.707%	$12.3109	$12.31	$12.30	$12.30
7 purchase totals =	$880.37		$942.1285	$942.12	$942.10	$942.00