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	$221.47	12.512%	$249.1803	$249.18	$249.20	$249.20
Purchase #2	$48.62	4.646%	$50.8789	$50.88	$50.90	$50.90
Purchase #3	$82.83	8.415%	$89.8001	$89.80	$89.80	$89.80
Purchase #4	$8.61	3.397%	$8.9025	$8.90	$8.90	$8.90
Purchase #5	$175.31	8.592%	$190.3726	$190.37	$190.35	$190.40
Purchase #6	$59.35	10.754%	$65.7325	$65.73	$65.75	$65.70
Purchase #7	$200.74	13.444%	$227.7275	$227.73	$227.75	$227.70
7 purchase totals =	$796.93		$882.5944	$882.59	$882.65	$882.60