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	$25.91	6.264%	$27.533	$27.53	$27.55	$27.50
Purchase #2	$130.26	10.236%	$143.5934	$143.59	$143.60	$143.60
Purchase #3	$109.47	8.861%	$119.1701	$119.17	$119.15	$119.20
Purchase #4	$210.48	5.522%	$222.1027	$222.10	$222.10	$222.10
Purchase #5	$221.98	12.370%	$249.4389	$249.44	$249.45	$249.40
Purchase #6	$215.48	10.170%	$237.3943	$237.39	$237.40	$237.40
Purchase #7	$70.36	3.653%	$72.9303	$72.93	$72.95	$72.90
7 purchase totals =	$983.94		$1,072.1627	$1,072.15	$1,072.20	$1,072.10