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	$79.45	5.586%	$83.8881	$83.89	$83.90	$83.90
Purchase #2	$23.76	9.767%	$26.0806	$26.08	$26.10	$26.10
Purchase #3	$228.38	13.114%	$258.3298	$258.33	$258.35	$258.30
Purchase #4	$183.72	9.305%	$200.8151	$200.82	$200.80	$200.80
Purchase #5	$249.90	3.182%	$257.8518	$257.85	$257.85	$257.90
Purchase #6	$75.49	12.808%	$85.1588	$85.16	$85.15	$85.20
Purchase #7	$82.66	9.544%	$90.5491	$90.55	$90.55	$90.50
7 purchase totals =	$923.36		$1,002.6733	$1,002.68	$1,002.70	$1,002.70