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	$163.98	5.132%	$172.3955	$172.40	$172.40	$172.40
Purchase #2	$136.83	9.811%	$150.2544	$150.25	$150.25	$150.30
Purchase #3	$232.94	9.821%	$255.817	$255.82	$255.80	$255.80
Purchase #4	$75.77	13.457%	$85.9664	$85.97	$85.95	$86.00
Purchase #5	$41.35	12.411%	$46.4819	$46.48	$46.50	$46.50
Purchase #6	$25.55	11.582%	$28.5092	$28.51	$28.50	$28.50
Purchase #7	$78.68	11.193%	$87.4867	$87.49	$87.50	$87.50
7 purchase totals =	$755.10		$826.9111	$826.92	$826.90	$827.00