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	$102.78	9.756%	$112.8072	$112.81	$112.80	$112.80
Purchase #2	$78.92	12.833%	$89.0478	$89.05	$89.05	$89.00
Purchase #3	$158.78	5.716%	$167.8559	$167.86	$167.85	$167.90
Purchase #4	$6.45	11.255%	$7.1759	$7.18	$7.20	$7.20
Purchase #5	$116.74	5.672%	$123.3615	$123.36	$123.35	$123.40
Purchase #6	$194.73	4.821%	$204.1179	$204.12	$204.10	$204.10
Purchase #7	$193.33	12.819%	$218.113	$218.11	$218.10	$218.10
7 purchase totals =	$851.73		$922.4792	$922.49	$922.45	$922.50