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	$12.45	7.423%	$13.3742	$13.37	$13.35	$13.40
Purchase #2	$166.48	9.844%	$182.8683	$182.87	$182.85	$182.90
Purchase #3	$220.47	7.305%	$236.5753	$236.58	$236.60	$236.60
Purchase #4	$182.31	12.353%	$204.8308	$204.83	$204.85	$204.80
Purchase #5	$29.57	4.426%	$30.8788	$30.88	$30.90	$30.90
Purchase #6	$223.68	12.134%	$250.8213	$250.82	$250.80	$250.80
Purchase #7	$53.73	10.134%	$59.175	$59.18	$59.20	$59.20
7 purchase totals =	$888.69		$978.5237	$978.53	$978.55	$978.60