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	$79.38	9.448%	$86.8798	$86.88	$86.90	$86.90
Purchase #2	$159.50	6.309%	$169.5629	$169.56	$169.55	$169.60
Purchase #3	$97.25	8.454%	$105.4715	$105.47	$105.45	$105.50
Purchase #4	$84.48	3.852%	$87.7342	$87.73	$87.75	$87.70
Purchase #5	$189.69	10.657%	$209.9053	$209.91	$209.90	$209.90
Purchase #6	$130.90	6.204%	$139.021	$139.02	$139.00	$139.00
Purchase #7	$91.51	10.300%	$100.9355	$100.94	$100.95	$100.90
7 purchase totals =	$832.71		$899.5102	$899.51	$899.50	$899.50