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	$100.76	10.407%	$111.2461	$111.25	$111.25	$111.20
Purchase #2	$206.53	4.813%	$216.4703	$216.47	$216.45	$216.50
Purchase #3	$12.32	4.354%	$12.8564	$12.86	$12.85	$12.90
Purchase #4	$135.70	13.271%	$153.7087	$153.71	$153.70	$153.70
Purchase #5	$124.95	13.220%	$141.4684	$141.47	$141.45	$141.50
Purchase #6	$169.33	10.318%	$186.8015	$186.80	$186.80	$186.80
Purchase #7	$69.69	11.696%	$77.8409	$77.84	$77.85	$77.80
7 purchase totals =	$819.28		$900.3923	$900.40	$900.35	$900.40