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	$135.33	12.574%	$152.3464	$152.35	$152.35	$152.30
Purchase #2	$113.51	13.510%	$128.8452	$128.85	$128.85	$128.80
Purchase #3	$145.83	3.466%	$150.8845	$150.88	$150.90	$150.90
Purchase #4	$30.67	12.834%	$34.6062	$34.61	$34.60	$34.60
Purchase #5	$19.44	8.660%	$21.1235	$21.12	$21.10	$21.10
Purchase #6	$93.72	8.361%	$101.5559	$101.56	$101.55	$101.60
Purchase #7	$51.55	9.286%	$56.3369	$56.34	$56.35	$56.30
7 purchase totals =	$590.05		$645.6986	$645.71	$645.70	$645.60