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	$250.43	5.575%	$264.3915	$264.39	$264.40	$264.40
Purchase #2	$249.48	5.430%	$263.0268	$263.03	$263.05	$263.00
Purchase #3	$190.90	10.144%	$210.2649	$210.26	$210.25	$210.30
Purchase #4	$40.70	13.561%	$46.2193	$46.22	$46.20	$46.20
Purchase #5	$141.98	6.473%	$151.1704	$151.17	$151.15	$151.20
Purchase #6	$72.36	5.607%	$76.4172	$76.42	$76.40	$76.40
Purchase #7	$85.29	3.131%	$87.9604	$87.96	$87.95	$88.00
7 purchase totals =	$1,031.14		$1,099.4505	$1,099.45	$1,099.40	$1,099.50