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	$176.44	7.522%	$189.7118	$189.71	$189.70	$189.70
Purchase #2	$183.46	3.328%	$189.5655	$189.57	$189.55	$189.60
Purchase #3	$243.25	4.779%	$254.8749	$254.87	$254.85	$254.90
Purchase #4	$234.87	10.820%	$260.2829	$260.28	$260.30	$260.30
Purchase #5	$126.59	8.734%	$137.6464	$137.65	$137.65	$137.60
Purchase #6	$228.32	3.765%	$236.9162	$236.92	$236.90	$236.90
Purchase #7	$207.85	11.375%	$231.4929	$231.49	$231.50	$231.50
7 purchase totals =	$1,400.78		$1,500.4906	$1,500.49	$1,500.45	$1,500.50