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	$113.36	12.319%	$127.3248	$127.32	$127.30	$127.30
Purchase #2	$51.51	9.696%	$56.5044	$56.50	$56.50	$56.50
Purchase #3	$156.69	7.739%	$168.8162	$168.82	$168.80	$168.80
Purchase #4	$44.80	4.276%	$46.7156	$46.72	$46.70	$46.70
Purchase #5	$156.25	5.714%	$165.1781	$165.18	$165.20	$165.20
Purchase #6	$24.61	4.650%	$25.7544	$25.75	$25.75	$25.80
Purchase #7	$87.97	12.243%	$98.7402	$98.74	$98.75	$98.70
7 purchase totals =	$635.19		$689.0337	$689.03	$689.00	$689.00