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	$18.35	9.248%	$20.047	$20.05	$20.05	$20.00
Purchase #2	$73.57	11.686%	$82.1674	$82.17	$82.15	$82.20
Purchase #3	$155.59	11.614%	$173.6602	$173.66	$173.65	$173.70
Purchase #4	$211.33	6.813%	$225.7279	$225.73	$225.75	$225.70
Purchase #5	$77.72	9.789%	$85.328	$85.33	$85.35	$85.30
Purchase #6	$16.56	3.337%	$17.1126	$17.11	$17.10	$17.10
Purchase #7	$69.34	4.338%	$72.348	$72.35	$72.35	$72.30
7 purchase totals =	$622.46		$676.3911	$676.40	$676.40	$676.30