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	$88.34	13.558%	$100.3171	$100.32	$100.30	$100.30
Purchase #2	$178.89	11.460%	$199.3908	$199.39	$199.40	$199.40
Purchase #3	$173.52	9.394%	$189.8205	$189.82	$189.80	$189.80
Purchase #4	$44.29	6.142%	$47.0103	$47.01	$47.00	$47.00
Purchase #5	$29.47	13.601%	$33.4782	$33.48	$33.50	$33.50
Purchase #6	$127.28	11.368%	$141.7492	$141.75	$141.75	$141.70
Purchase #7	$49.41	6.573%	$52.6577	$52.66	$52.65	$52.70
7 purchase totals =	$691.20		$764.4238	$764.43	$764.40	$764.40