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	$14.59	4.270%	$15.213	$15.21	$15.20	$15.20
Purchase #2	$82.76	8.125%	$89.4843	$89.48	$89.50	$89.50
Purchase #3	$232.59	10.805%	$257.7213	$257.72	$257.70	$257.70
Purchase #4	$117.44	3.110%	$121.0924	$121.09	$121.10	$121.10
Purchase #5	$22.69	13.669%	$25.7915	$25.79	$25.80	$25.80
Purchase #6	$165.92	3.410%	$171.5779	$171.58	$171.60	$171.60
Purchase #7	$78.57	9.313%	$85.8872	$85.89	$85.90	$85.90
7 purchase totals =	$714.56		$766.7676	$766.76	$766.80	$766.80