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	$84.43	7.631%	$90.8729	$90.87	$90.85	$90.90
Purchase #2	$243.38	13.601%	$276.4821	$276.48	$276.50	$276.50
Purchase #3	$250.30	11.209%	$278.3561	$278.36	$278.35	$278.40
Purchase #4	$92.98	11.869%	$104.0158	$104.02	$104.00	$104.00
Purchase #5	$51.29	10.626%	$56.7401	$56.74	$56.75	$56.70
Purchase #6	$138.82	4.194%	$144.6421	$144.64	$144.65	$144.60
Purchase #7	$176.29	13.241%	$199.6326	$199.63	$199.65	$199.60
7 purchase totals =	$1,037.49		$1,150.7417	$1,150.74	$1,150.75	$1,150.70