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	$199.41	12.291%	$223.9195	$223.92	$223.90	$223.90
Purchase #2	$139.76	6.534%	$148.8919	$148.89	$148.90	$148.90
Purchase #3	$46.37	4.221%	$48.3273	$48.33	$48.35	$48.30
Purchase #4	$131.75	6.856%	$140.7828	$140.78	$140.80	$140.80
Purchase #5	$232.61	6.154%	$246.9248	$246.92	$246.90	$246.90
Purchase #6	$92.39	4.785%	$96.8109	$96.81	$96.80	$96.80
Purchase #7	$214.28	3.526%	$221.8355	$221.84	$221.85	$221.80
7 purchase totals =	$1,056.57		$1,127.4927	$1,127.49	$1,127.50	$1,127.40