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	$183.45	6.782%	$195.8916	$195.89	$195.90	$195.90
Purchase #2	$62.28	4.290%	$64.9518	$64.95	$64.95	$65.00
Purchase #3	$145.37	6.550%	$154.8917	$154.89	$154.90	$154.90
Purchase #4	$98.60	11.159%	$109.6028	$109.60	$109.60	$109.60
Purchase #5	$100.28	11.474%	$111.7861	$111.79	$111.80	$111.80
Purchase #6	$127.43	13.832%	$145.0561	$145.06	$145.05	$145.10
Purchase #7	$196.44	6.759%	$209.7174	$209.72	$209.70	$209.70
7 purchase totals =	$913.85		$991.8975	$991.90	$991.90	$992.00