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	$44.48	12.368%	$49.9813	$49.98	$50.00	$50.00
Purchase #2	$227.65	13.521%	$258.4306	$258.43	$258.45	$258.40
Purchase #3	$170.92	11.547%	$190.6561	$190.66	$190.65	$190.70
Purchase #4	$162.34	10.809%	$179.8873	$179.89	$179.90	$179.90
Purchase #5	$162.33	7.389%	$174.3246	$174.32	$174.30	$174.30
Purchase #6	$142.77	10.864%	$158.2805	$158.28	$158.30	$158.30
Purchase #7	$71.64	11.201%	$79.6644	$79.66	$79.65	$79.70
7 purchase totals =	$982.13		$1,091.2248	$1,091.22	$1,091.25	$1,091.30