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	$46.64	12.106%	$52.2862	$52.29	$52.30	$52.30
Purchase #2	$113.42	9.651%	$124.3662	$124.37	$124.35	$124.40
Purchase #3	$82.66	12.167%	$92.7172	$92.72	$92.70	$92.70
Purchase #4	$101.91	10.751%	$112.8663	$112.87	$112.85	$112.90
Purchase #5	$60.98	10.769%	$67.5469	$67.55	$67.55	$67.50
Purchase #6	$98.66	4.311%	$102.9132	$102.91	$102.90	$102.90
Purchase #7	$52.74	13.184%	$59.6932	$59.69	$59.70	$59.70
7 purchase totals =	$557.01		$612.3892	$612.40	$612.35	$612.40