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	$81.55	5.305%	$85.8762	$85.88	$85.90	$85.90
Purchase #2	$230.58	12.817%	$260.1334	$260.13	$260.15	$260.10
Purchase #3	$63.80	6.538%	$67.9712	$67.97	$67.95	$68.00
Purchase #4	$45.41	9.550%	$49.7467	$49.75	$49.75	$49.70
Purchase #5	$99.27	4.656%	$103.892	$103.89	$103.90	$103.90
Purchase #6	$91.75	9.635%	$100.5901	$100.59	$100.60	$100.60
Purchase #7	$215.82	12.717%	$243.2658	$243.27	$243.25	$243.30
7 purchase totals =	$828.18		$911.4754	$911.48	$911.50	$911.50