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	$168.98	9.716%	$185.3981	$185.40	$185.40	$185.40
Purchase #2	$78.50	6.473%	$83.5813	$83.58	$83.60	$83.60
Purchase #3	$72.93	8.299%	$78.9825	$78.98	$79.00	$79.00
Purchase #4	$40.72	13.634%	$46.2718	$46.27	$46.25	$46.30
Purchase #5	$109.54	13.311%	$124.1209	$124.12	$124.10	$124.10
Purchase #6	$8.58	3.453%	$8.8763	$8.88	$8.90	$8.90
Purchase #7	$29.48	12.223%	$33.0833	$33.08	$33.10	$33.10
7 purchase totals =	$508.73		$560.3142	$560.31	$560.35	$560.40