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	$87.73	11.223%	$97.5759	$97.58	$97.60	$97.60
Purchase #2	$192.86	6.466%	$205.3303	$205.33	$205.35	$205.30
Purchase #3	$59.56	5.121%	$62.6101	$62.61	$62.60	$62.60
Purchase #4	$119.66	12.720%	$134.8808	$134.88	$134.90	$134.90
Purchase #5	$26.57	12.556%	$29.9061	$29.91	$29.90	$29.90
Purchase #6	$80.35	11.843%	$89.8659	$89.87	$89.85	$89.90
Purchase #7	$74.62	7.232%	$80.0165	$80.02	$80.00	$80.00
7 purchase totals =	$641.35		$700.1856	$700.20	$700.20	$700.20