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	$132.71	13.793%	$151.0147	$151.01	$151.00	$151.00
Purchase #2	$225.99	3.426%	$233.7324	$233.73	$233.75	$233.70
Purchase #3	$155.62	13.310%	$176.333	$176.33	$176.35	$176.30
Purchase #4	$85.58	7.621%	$92.1021	$92.10	$92.10	$92.10
Purchase #5	$162.51	5.745%	$171.8462	$171.85	$171.85	$171.80
Purchase #6	$45.46	4.525%	$47.5171	$47.52	$47.50	$47.50
Purchase #7	$39.97	6.208%	$42.4513	$42.45	$42.45	$42.50
7 purchase totals =	$847.84		$914.9968	$914.99	$915.00	$914.90