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	$183.26	13.586%	$208.1577	$208.16	$208.15	$208.20
Purchase #2	$194.83	11.815%	$217.8492	$217.85	$217.85	$217.80
Purchase #3	$53.25	3.403%	$55.0621	$55.06	$55.05	$55.10
Purchase #4	$50.57	4.624%	$52.9084	$52.91	$52.90	$52.90
Purchase #5	$65.77	6.654%	$70.1463	$70.15	$70.15	$70.10
Purchase #6	$96.83	8.496%	$105.0567	$105.06	$105.05	$105.10
Purchase #7	$43.98	3.136%	$45.3592	$45.36	$45.35	$45.40
7 purchase totals =	$688.49		$754.5396	$754.55	$754.50	$754.60