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	$53.60	6.140%	$56.891	$56.89	$56.90	$56.90
Purchase #2	$195.67	12.731%	$220.5807	$220.58	$220.60	$220.60
Purchase #3	$141.60	10.255%	$156.1211	$156.12	$156.10	$156.10
Purchase #4	$42.68	11.243%	$47.4785	$47.48	$47.50	$47.50
Purchase #5	$56.60	6.581%	$60.3248	$60.32	$60.30	$60.30
Purchase #6	$56.46	5.565%	$59.602	$59.60	$59.60	$59.60
Purchase #7	$218.91	7.276%	$234.8379	$234.84	$234.85	$234.80
7 purchase totals =	$765.52		$835.8360	$835.83	$835.85	$835.80