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	$131.41	4.543%	$137.38	$137.38	$137.40	$137.40
Purchase #2	$82.81	9.117%	$90.3598	$90.36	$90.35	$90.40
Purchase #3	$40.47	12.332%	$45.4608	$45.46	$45.45	$45.50
Purchase #4	$224.91	10.250%	$247.9633	$247.96	$247.95	$248.00
Purchase #5	$89.57	11.680%	$100.0318	$100.03	$100.05	$100.00
Purchase #6	$112.37	4.266%	$117.1637	$117.16	$117.15	$117.20
Purchase #7	$185.30	13.657%	$210.6064	$210.61	$210.60	$210.60
7 purchase totals =	$866.84		$948.9658	$948.96	$948.95	$949.10