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	$171.96	4.277%	$179.3147	$179.31	$179.30	$179.30
Purchase #2	$151.38	10.231%	$166.8677	$166.87	$166.85	$166.90
Purchase #3	$135.68	13.685%	$154.2478	$154.25	$154.25	$154.20
Purchase #4	$78.57	13.456%	$89.1424	$89.14	$89.15	$89.10
Purchase #5	$46.48	13.442%	$52.7278	$52.73	$52.75	$52.70
Purchase #6	$47.34	8.403%	$51.318	$51.32	$51.30	$51.30
Purchase #7	$243.29	7.756%	$262.1596	$262.16	$262.15	$262.20
7 purchase totals =	$874.70		$955.7780	$955.78	$955.75	$955.70