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	$36.98	8.555%	$40.1436	$40.14	$40.15	$40.10
Purchase #2	$78.87	12.475%	$88.709	$88.71	$88.70	$88.70
Purchase #3	$168.92	12.471%	$189.986	$189.99	$190.00	$190.00
Purchase #4	$154.66	11.764%	$172.8542	$172.85	$172.85	$172.90
Purchase #5	$91.57	5.477%	$96.5853	$96.59	$96.60	$96.60
Purchase #6	$81.34	10.779%	$90.1076	$90.11	$90.10	$90.10
Purchase #7	$109.52	11.467%	$122.0787	$122.08	$122.10	$122.10
7 purchase totals =	$721.86		$800.4644	$800.47	$800.50	$800.50