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	$195.88	10.159%	$215.7794	$215.78	$215.80	$215.80
Purchase #2	$190.84	5.266%	$200.8896	$200.89	$200.90	$200.90
Purchase #3	$145.25	4.748%	$152.1465	$152.15	$152.15	$152.10
Purchase #4	$61.33	8.109%	$66.3032	$66.30	$66.30	$66.30
Purchase #5	$106.62	10.751%	$118.0827	$118.08	$118.10	$118.10
Purchase #6	$35.30	4.449%	$36.8705	$36.87	$36.85	$36.90
Purchase #7	$28.90	3.300%	$29.8537	$29.85	$29.85	$29.90
7 purchase totals =	$764.12		$819.9256	$819.92	$819.95	$820.00