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	$183.65	12.317%	$206.2702	$206.27	$206.25	$206.30
Purchase #2	$162.28	10.234%	$178.8877	$178.89	$178.90	$178.90
Purchase #3	$6.33	13.493%	$7.1841	$7.18	$7.20	$7.20
Purchase #4	$225.51	3.386%	$233.1458	$233.15	$233.15	$233.10
Purchase #5	$172.53	8.728%	$187.5884	$187.59	$187.60	$187.60
Purchase #6	$185.45	13.140%	$209.8181	$209.82	$209.80	$209.80
Purchase #7	$57.60	6.412%	$61.2933	$61.29	$61.30	$61.30
7 purchase totals =	$993.35		$1,084.1876	$1,084.19	$1,084.20	$1,084.20