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	$91.90	10.528%	$101.5752	$101.58	$101.60	$101.60
Purchase #2	$12.78	12.729%	$14.4068	$14.41	$14.40	$14.40
Purchase #3	$225.32	10.704%	$249.4383	$249.44	$249.45	$249.40
Purchase #4	$62.38	6.485%	$66.4253	$66.43	$66.45	$66.40
Purchase #5	$55.91	9.764%	$61.3691	$61.37	$61.35	$61.40
Purchase #6	$88.31	7.223%	$94.6886	$94.69	$94.70	$94.70
Purchase #7	$205.41	3.628%	$212.8623	$212.86	$212.85	$212.90
7 purchase totals =	$742.01		$800.7656	$800.78	$800.80	$800.80