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	$50.54	7.518%	$54.3396	$54.34	$54.35	$54.30
Purchase #2	$196.54	9.422%	$215.058	$215.06	$215.05	$215.10
Purchase #3	$88.39	3.834%	$91.7789	$91.78	$91.80	$91.80
Purchase #4	$101.95	8.546%	$110.6626	$110.66	$110.65	$110.70
Purchase #5	$56.98	8.643%	$61.9048	$61.90	$61.90	$61.90
Purchase #6	$90.83	8.578%	$98.6214	$98.62	$98.60	$98.60
Purchase #7	$181.40	13.810%	$206.4513	$206.45	$206.45	$206.50
7 purchase totals =	$766.63		$838.8166	$838.81	$838.80	$838.90