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	$186.60	5.136%	$196.1838	$196.18	$196.20	$196.20
Purchase #2	$104.53	9.202%	$114.1489	$114.15	$114.15	$114.10
Purchase #3	$90.51	6.319%	$96.2293	$96.23	$96.25	$96.20
Purchase #4	$73.59	13.659%	$83.6417	$83.64	$83.65	$83.60
Purchase #5	$53.72	10.153%	$59.1742	$59.17	$59.15	$59.20
Purchase #6	$63.86	9.321%	$69.8124	$69.81	$69.80	$69.80
Purchase #7	$109.35	11.305%	$121.712	$121.71	$121.70	$121.70
7 purchase totals =	$682.16		$740.9023	$740.89	$740.90	$740.80