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	$144.25	12.810%	$162.7284	$162.73	$162.75	$162.70
Purchase #2	$125.88	11.430%	$140.2681	$140.27	$140.25	$140.30
Purchase #3	$210.81	11.160%	$234.3364	$234.34	$234.35	$234.30
Purchase #4	$91.38	13.722%	$103.9192	$103.92	$103.90	$103.90
Purchase #5	$56.65	8.109%	$61.2437	$61.24	$61.25	$61.20
Purchase #6	$49.70	9.299%	$54.3216	$54.32	$54.30	$54.30
Purchase #7	$216.65	5.850%	$229.324	$229.32	$229.30	$229.30
7 purchase totals =	$895.32		$986.1414	$986.14	$986.10	$986.00