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	$244.84	3.227%	$252.741	$252.74	$252.75	$252.70
Purchase #2	$153.83	12.334%	$172.8034	$172.80	$172.80	$172.80
Purchase #3	$139.78	10.808%	$154.8874	$154.89	$154.90	$154.90
Purchase #4	$140.88	9.284%	$153.9593	$153.96	$153.95	$154.00
Purchase #5	$200.51	9.670%	$219.8993	$219.90	$219.90	$219.90
Purchase #6	$27.33	5.526%	$28.8403	$28.84	$28.85	$28.80
Purchase #7	$18.75	8.661%	$20.3739	$20.37	$20.35	$20.40
7 purchase totals =	$925.92		$1,003.5046	$1,003.50	$1,003.50	$1,003.50