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	$78.65	12.251%	$88.2854	$88.29	$88.30	$88.30
Purchase #2	$45.50	11.816%	$50.8763	$50.88	$50.90	$50.90
Purchase #3	$40.78	12.506%	$45.8799	$45.88	$45.90	$45.90
Purchase #4	$223.80	4.712%	$234.3455	$234.35	$234.35	$234.30
Purchase #5	$111.66	4.655%	$116.8578	$116.86	$116.85	$116.90
Purchase #6	$40.84	4.670%	$42.7472	$42.75	$42.75	$42.70
Purchase #7	$39.85	10.677%	$44.1048	$44.10	$44.10	$44.10
7 purchase totals =	$581.08		$623.0969	$623.11	$623.15	$623.10