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	$169.45	12.562%	$190.7363	$190.74	$190.75	$190.70
Purchase #2	$117.92	11.226%	$131.1577	$131.16	$131.15	$131.20
Purchase #3	$26.34	12.492%	$29.6304	$29.63	$29.65	$29.60
Purchase #4	$118.25	11.506%	$131.8558	$131.86	$131.85	$131.90
Purchase #5	$105.79	3.526%	$109.5202	$109.52	$109.50	$109.50
Purchase #6	$27.43	5.123%	$28.8352	$28.84	$28.85	$28.80
Purchase #7	$182.32	10.754%	$201.9267	$201.93	$201.95	$201.90
7 purchase totals =	$747.50		$823.6623	$823.68	$823.70	$823.60