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	$166.71	7.576%	$179.3399	$179.34	$179.35	$179.30
Purchase #2	$215.68	4.500%	$225.3856	$225.39	$225.40	$225.40
Purchase #3	$62.50	4.549%	$65.3431	$65.34	$65.35	$65.30
Purchase #4	$80.41	10.715%	$89.0259	$89.03	$89.05	$89.00
Purchase #5	$136.93	9.352%	$149.7357	$149.74	$149.75	$149.70
Purchase #6	$27.63	6.874%	$29.5293	$29.53	$29.55	$29.50
Purchase #7	$58.92	6.149%	$62.543	$62.54	$62.55	$62.50
7 purchase totals =	$748.78		$800.9025	$800.91	$801.00	$800.70