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	$235.98	12.249%	$264.8852	$264.89	$264.90	$264.90
Purchase #2	$51.81	7.320%	$55.6025	$55.60	$55.60	$55.60
Purchase #3	$185.93	9.328%	$203.2736	$203.27	$203.25	$203.30
Purchase #4	$172.31	9.436%	$188.5692	$188.57	$188.55	$188.60
Purchase #5	$214.29	4.452%	$223.8302	$223.83	$223.85	$223.80
Purchase #6	$67.64	9.703%	$74.2031	$74.20	$74.20	$74.20
Purchase #7	$112.27	5.274%	$118.1911	$118.19	$118.20	$118.20
7 purchase totals =	$1,040.23		$1,128.5549	$1,128.55	$1,128.55	$1,128.60