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	$238.83	12.221%	$268.0174	$268.02	$268.00	$268.00
Purchase #2	$152.58	13.616%	$173.3553	$173.36	$173.35	$173.40
Purchase #3	$242.30	10.536%	$267.8287	$267.83	$267.85	$267.80
Purchase #4	$193.48	12.870%	$218.3809	$218.38	$218.40	$218.40
Purchase #5	$139.76	6.404%	$148.7102	$148.71	$148.70	$148.70
Purchase #6	$156.52	9.734%	$171.7557	$171.76	$171.75	$171.80
Purchase #7	$175.32	3.719%	$181.8402	$181.84	$181.85	$181.80
7 purchase totals =	$1,298.79		$1,429.8884	$1,429.90	$1,429.90	$1,429.90