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	$96.25	4.680%	$100.7545	$100.75	$100.75	$100.80
Purchase #2	$94.87	7.640%	$102.1181	$102.12	$102.10	$102.10
Purchase #3	$122.59	13.394%	$139.0097	$139.01	$139.00	$139.00
Purchase #4	$127.32	4.126%	$132.5732	$132.57	$132.55	$132.60
Purchase #5	$116.25	13.742%	$132.2251	$132.23	$132.25	$132.20
Purchase #6	$240.98	3.855%	$250.2698	$250.27	$250.25	$250.30
Purchase #7	$248.37	4.660%	$259.944	$259.94	$259.95	$259.90
7 purchase totals =	$1,046.63		$1,116.8944	$1,116.89	$1,116.85	$1,116.90