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	$237.71	8.722%	$258.4431	$258.44	$258.45	$258.40
Purchase #2	$89.91	9.363%	$98.3283	$98.33	$98.35	$98.30
Purchase #3	$82.83	4.847%	$86.8448	$86.84	$86.85	$86.80
Purchase #4	$233.36	6.517%	$248.5681	$248.57	$248.55	$248.60
Purchase #5	$20.35	10.333%	$22.4528	$22.45	$22.45	$22.50
Purchase #6	$164.95	13.769%	$187.662	$187.66	$187.65	$187.70
Purchase #7	$91.34	10.194%	$100.6512	$100.65	$100.65	$100.70
7 purchase totals =	$920.45		$1,002.9503	$1,002.94	$1,002.95	$1,003.00