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	$84.57	6.868%	$90.3783	$90.38	$90.40	$90.40
Purchase #2	$154.49	8.103%	$167.0083	$167.01	$167.00	$167.00
Purchase #3	$11.59	12.554%	$13.045	$13.05	$13.05	$13.00
Purchase #4	$53.29	8.384%	$57.7578	$57.76	$57.75	$57.80
Purchase #5	$169.28	10.616%	$187.2508	$187.25	$187.25	$187.30
Purchase #6	$106.40	10.250%	$117.306	$117.31	$117.30	$117.30
Purchase #7	$81.35	10.553%	$89.9349	$89.93	$89.95	$89.90
7 purchase totals =	$660.97		$722.6811	$722.69	$722.70	$722.70