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	$30.32	9.189%	$33.1061	$33.11	$33.10	$33.10
Purchase #2	$151.56	13.831%	$172.5223	$172.52	$172.50	$172.50
Purchase #3	$79.78	3.811%	$82.8204	$82.82	$82.80	$82.80
Purchase #4	$211.38	6.870%	$225.9018	$225.90	$225.90	$225.90
Purchase #5	$39.45	8.730%	$42.894	$42.89	$42.90	$42.90
Purchase #6	$164.47	3.436%	$170.1212	$170.12	$170.10	$170.10
Purchase #7	$118.37	4.128%	$123.2563	$123.26	$123.25	$123.30
7 purchase totals =	$795.33		$850.6221	$850.62	$850.55	$850.60