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	$183.30	12.644%	$206.4765	$206.48	$206.50	$206.50
Purchase #2	$244.51	4.781%	$256.2	$256.20	$256.20	$256.20
Purchase #3	$186.74	5.256%	$196.5551	$196.56	$196.55	$196.60
Purchase #4	$143.52	3.210%	$148.127	$148.13	$148.15	$148.10
Purchase #5	$21.75	12.581%	$24.4864	$24.49	$24.50	$24.50
Purchase #6	$230.75	5.507%	$243.4574	$243.46	$243.45	$243.50
Purchase #7	$40.38	5.279%	$42.5117	$42.51	$42.50	$42.50
7 purchase totals =	$1,050.95		$1,117.8141	$1,117.83	$1,117.85	$1,117.90