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	$238.52	10.864%	$264.4328	$264.43	$264.45	$264.40
Purchase #2	$112.74	5.402%	$118.8302	$118.83	$118.85	$118.80
Purchase #3	$191.95	3.172%	$198.0387	$198.04	$198.05	$198.00
Purchase #4	$52.72	12.490%	$59.3047	$59.30	$59.30	$59.30
Purchase #5	$179.93	4.668%	$188.3291	$188.33	$188.35	$188.30
Purchase #6	$8.43	13.792%	$9.5927	$9.59	$9.60	$9.60
Purchase #7	$39.35	4.404%	$41.083	$41.08	$41.10	$41.10
7 purchase totals =	$823.64		$879.6112	$879.60	$879.70	$879.50