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	$35.79	6.545%	$38.1325	$38.13	$38.15	$38.10
Purchase #2	$64.44	4.355%	$67.2464	$67.25	$67.25	$67.20
Purchase #3	$143.81	8.568%	$156.1316	$156.13	$156.15	$156.10
Purchase #4	$13.32	3.846%	$13.8323	$13.83	$13.85	$13.80
Purchase #5	$131.78	9.641%	$144.4849	$144.48	$144.50	$144.50
Purchase #6	$165.94	8.819%	$180.5742	$180.57	$180.55	$180.60
Purchase #7	$249.37	10.667%	$275.9703	$275.97	$275.95	$276.00
7 purchase totals =	$804.45		$876.3722	$876.36	$876.40	$876.30