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	$167.59	5.566%	$176.9181	$176.92	$176.90	$176.90
Purchase #2	$77.83	3.862%	$80.8358	$80.84	$80.85	$80.80
Purchase #3	$77.96	3.770%	$80.8991	$80.90	$80.90	$80.90
Purchase #4	$128.45	8.444%	$139.2963	$139.30	$139.30	$139.30
Purchase #5	$143.57	11.154%	$159.5838	$159.58	$159.60	$159.60
Purchase #6	$55.99	9.424%	$61.2665	$61.27	$61.25	$61.30
Purchase #7	$90.50	9.799%	$99.3681	$99.37	$99.35	$99.40
7 purchase totals =	$741.89		$798.1677	$798.18	$798.15	$798.20