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	$97.64	12.554%	$109.8977	$109.90	$109.90	$109.90
Purchase #2	$215.52	3.115%	$222.2334	$222.23	$222.25	$222.20
Purchase #3	$210.39	3.280%	$217.2908	$217.29	$217.30	$217.30
Purchase #4	$16.39	12.288%	$18.404	$18.40	$18.40	$18.40
Purchase #5	$29.95	4.142%	$31.1905	$31.19	$31.20	$31.20
Purchase #6	$83.89	7.528%	$90.2052	$90.21	$90.20	$90.20
Purchase #7	$129.30	4.758%	$135.4521	$135.45	$135.45	$135.50
7 purchase totals =	$783.08		$824.6737	$824.67	$824.70	$824.70