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	$249.67	8.304%	$270.4026	$270.40	$270.40	$270.40
Purchase #2	$78.81	8.773%	$85.724	$85.72	$85.70	$85.70
Purchase #3	$99.32	10.741%	$109.988	$109.99	$110.00	$110.00
Purchase #4	$151.31	11.651%	$168.9391	$168.94	$168.95	$168.90
Purchase #5	$210.73	8.128%	$227.8581	$227.86	$227.85	$227.90
Purchase #6	$247.39	3.338%	$255.6479	$255.65	$255.65	$255.60
Purchase #7	$121.49	12.127%	$136.2231	$136.22	$136.20	$136.20
7 purchase totals =	$1,158.72		$1,254.7828	$1,254.78	$1,254.75	$1,254.70