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	$188.73	4.324%	$196.8907	$196.89	$196.90	$196.90
Purchase #2	$161.54	5.329%	$170.1485	$170.15	$170.15	$170.10
Purchase #3	$41.72	12.772%	$47.0485	$47.05	$47.05	$47.00
Purchase #4	$169.96	13.113%	$192.2469	$192.25	$192.25	$192.20
Purchase #5	$249.51	5.555%	$263.3703	$263.37	$263.35	$263.40
Purchase #6	$207.60	6.201%	$220.4733	$220.47	$220.45	$220.50
Purchase #7	$115.90	13.329%	$131.3483	$131.35	$131.35	$131.30
7 purchase totals =	$1,134.96		$1,221.5265	$1,221.53	$1,221.50	$1,221.40