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	$198.37	3.773%	$205.8545	$205.85	$205.85	$205.90
Purchase #2	$89.55	13.601%	$101.7297	$101.73	$101.75	$101.70
Purchase #3	$80.89	10.662%	$89.5145	$89.51	$89.50	$89.50
Purchase #4	$36.91	6.186%	$39.1933	$39.19	$39.20	$39.20
Purchase #5	$76.49	6.171%	$81.2102	$81.21	$81.20	$81.20
Purchase #6	$63.80	7.335%	$68.4797	$68.48	$68.50	$68.50
Purchase #7	$80.69	11.296%	$89.8047	$89.80	$89.80	$89.80
7 purchase totals =	$626.70		$675.7866	$675.77	$675.80	$675.80