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	$84.38	7.615%	$90.8055	$90.81	$90.80	$90.80
Purchase #2	$185.46	13.441%	$210.3877	$210.39	$210.40	$210.40
Purchase #3	$198.97	4.319%	$207.5635	$207.56	$207.55	$207.60
Purchase #4	$56.29	5.751%	$59.5272	$59.53	$59.55	$59.50
Purchase #5	$26.30	8.431%	$28.5174	$28.52	$28.50	$28.50
Purchase #6	$135.34	9.786%	$148.5844	$148.58	$148.60	$148.60
Purchase #7	$21.56	10.570%	$23.8389	$23.84	$23.85	$23.80
7 purchase totals =	$708.30		$769.2246	$769.23	$769.25	$769.20