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	$148.86	5.356%	$156.8329	$156.83	$156.85	$156.80
Purchase #2	$61.88	9.374%	$67.6806	$67.68	$67.70	$67.70
Purchase #3	$43.76	11.782%	$48.9158	$48.92	$48.90	$48.90
Purchase #4	$139.65	11.874%	$156.232	$156.23	$156.25	$156.20
Purchase #5	$78.37	4.119%	$81.5981	$81.60	$81.60	$81.60
Purchase #6	$37.83	10.650%	$41.8589	$41.86	$41.85	$41.90
Purchase #7	$51.57	13.432%	$58.4969	$58.50	$58.50	$58.50
7 purchase totals =	$561.92		$611.6152	$611.62	$611.65	$611.60