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	$141.92	3.277%	$146.5707	$146.57	$146.55	$146.60
Purchase #2	$91.89	6.124%	$97.5173	$97.52	$97.50	$97.50
Purchase #3	$83.69	6.531%	$89.1558	$89.16	$89.15	$89.20
Purchase #4	$45.52	3.552%	$47.1369	$47.14	$47.15	$47.10
Purchase #5	$206.65	11.145%	$229.6811	$229.68	$229.70	$229.70
Purchase #6	$223.74	9.218%	$244.3644	$244.36	$244.35	$244.40
Purchase #7	$82.88	7.518%	$89.1109	$89.11	$89.10	$89.10
7 purchase totals =	$876.29		$943.5371	$943.54	$943.50	$943.60