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	$133.83	10.345%	$147.6747	$147.67	$147.65	$147.70
Purchase #2	$53.33	6.801%	$56.957	$56.96	$56.95	$57.00
Purchase #3	$39.97	4.874%	$41.9181	$41.92	$41.90	$41.90
Purchase #4	$137.38	9.323%	$150.1879	$150.19	$150.20	$150.20
Purchase #5	$53.38	5.378%	$56.2508	$56.25	$56.25	$56.30
Purchase #6	$13.71	4.682%	$14.3519	$14.35	$14.35	$14.40
Purchase #7	$116.91	5.735%	$123.6148	$123.61	$123.60	$123.60
7 purchase totals =	$548.51		$590.9552	$590.95	$590.90	$591.10