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	$17.53	6.423%	$18.656	$18.66	$18.65	$18.70
Purchase #2	$39.48	13.716%	$44.8951	$44.90	$44.90	$44.90
Purchase #3	$10.49	9.771%	$11.515	$11.52	$11.50	$11.50
Purchase #4	$225.86	8.432%	$244.9045	$244.90	$244.90	$244.90
Purchase #5	$247.80	11.531%	$276.3738	$276.37	$276.35	$276.40
Purchase #6	$47.67	10.196%	$52.5304	$52.53	$52.55	$52.50
Purchase #7	$77.83	10.359%	$85.8924	$85.89	$85.90	$85.90
7 purchase totals =	$666.66		$734.7672	$734.77	$734.75	$734.80