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	$37.85	10.707%	$41.9026	$41.90	$41.90	$41.90
Purchase #2	$40.26	6.300%	$42.7964	$42.80	$42.80	$42.80
Purchase #3	$173.35	12.646%	$195.2718	$195.27	$195.25	$195.30
Purchase #4	$211.37	5.387%	$222.7565	$222.76	$222.75	$222.80
Purchase #5	$109.78	13.122%	$124.1853	$124.19	$124.20	$124.20
Purchase #6	$82.47	3.583%	$85.4249	$85.42	$85.40	$85.40
Purchase #7	$8.64	10.299%	$9.5298	$9.53	$9.55	$9.50
7 purchase totals =	$663.72		$721.8673	$721.87	$721.85	$721.90