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	$112.64	6.692%	$120.1779	$120.18	$120.20	$120.20
Purchase #2	$51.47	13.593%	$58.4663	$58.47	$58.45	$58.50
Purchase #3	$38.88	9.313%	$42.5009	$42.50	$42.50	$42.50
Purchase #4	$27.47	8.803%	$29.8882	$29.89	$29.90	$29.90
Purchase #5	$166.51	4.685%	$174.311	$174.31	$174.30	$174.30
Purchase #6	$194.90	12.506%	$219.2742	$219.27	$219.25	$219.30
Purchase #7	$96.85	8.457%	$105.0406	$105.04	$105.05	$105.00
7 purchase totals =	$688.72		$749.6591	$749.66	$749.65	$749.70