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	$27.38	9.417%	$29.9584	$29.96	$29.95	$30.00
Purchase #2	$145.90	10.607%	$161.3756	$161.38	$161.40	$161.40
Purchase #3	$37.46	3.280%	$38.6887	$38.69	$38.70	$38.70
Purchase #4	$196.41	7.615%	$211.3666	$211.37	$211.35	$211.40
Purchase #5	$19.54	6.698%	$20.8488	$20.85	$20.85	$20.80
Purchase #6	$223.29	11.726%	$249.473	$249.47	$249.45	$249.50
Purchase #7	$62.61	4.705%	$65.5558	$65.56	$65.55	$65.60
7 purchase totals =	$712.59		$777.2669	$777.28	$777.25	$777.40