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	$76.89	4.216%	$80.1317	$80.13	$80.15	$80.10
Purchase #2	$200.53	7.650%	$215.8705	$215.87	$215.85	$215.90
Purchase #3	$46.95	13.609%	$53.3394	$53.34	$53.35	$53.30
Purchase #4	$96.88	8.182%	$104.8067	$104.81	$104.80	$104.80
Purchase #5	$66.58	12.654%	$75.005	$75.01	$75.00	$75.00
Purchase #6	$148.39	8.152%	$160.4868	$160.49	$160.50	$160.50
Purchase #7	$209.38	11.694%	$233.8649	$233.86	$233.85	$233.90
7 purchase totals =	$845.60		$923.5050	$923.51	$923.50	$923.50