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	$243.61	9.786%	$267.4497	$267.45	$267.45	$267.40
Purchase #2	$121.72	4.796%	$127.5577	$127.56	$127.55	$127.60
Purchase #3	$86.30	4.222%	$89.9436	$89.94	$89.95	$89.90
Purchase #4	$170.89	10.716%	$189.2026	$189.20	$189.20	$189.20
Purchase #5	$89.59	12.360%	$100.6633	$100.66	$100.65	$100.70
Purchase #6	$206.38	7.304%	$221.454	$221.45	$221.45	$221.50
Purchase #7	$20.38	7.274%	$21.8624	$21.86	$21.85	$21.90
7 purchase totals =	$938.87		$1,018.1333	$1,018.12	$1,018.10	$1,018.20