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	$166.39	11.467%	$185.4699	$185.47	$185.45	$185.50
Purchase #2	$69.66	9.118%	$76.0116	$76.01	$76.00	$76.00
Purchase #3	$67.72	13.626%	$76.9475	$76.95	$76.95	$76.90
Purchase #4	$42.79	6.830%	$45.7126	$45.71	$45.70	$45.70
Purchase #5	$39.75	4.598%	$41.5777	$41.58	$41.60	$41.60
Purchase #6	$76.47	4.368%	$79.8102	$79.81	$79.80	$79.80
Purchase #7	$19.38	4.468%	$20.2459	$20.25	$20.25	$20.20
7 purchase totals =	$482.16		$525.7754	$525.78	$525.75	$525.70