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	$246.72	6.676%	$263.191	$263.19	$263.20	$263.20
Purchase #2	$56.73	12.779%	$63.9795	$63.98	$64.00	$64.00
Purchase #3	$118.59	11.569%	$132.3097	$132.31	$132.30	$132.30
Purchase #4	$90.29	5.195%	$94.9806	$94.98	$95.00	$95.00
Purchase #5	$67.85	5.208%	$71.3836	$71.38	$71.40	$71.40
Purchase #6	$155.48	11.171%	$172.8487	$172.85	$172.85	$172.80
Purchase #7	$183.64	3.762%	$190.5485	$190.55	$190.55	$190.50
7 purchase totals =	$919.30		$989.2416	$989.24	$989.30	$989.20