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	$177.90	12.603%	$200.3207	$200.32	$200.30	$200.30
Purchase #2	$148.33	13.735%	$168.7031	$168.70	$168.70	$168.70
Purchase #3	$9.88	9.515%	$10.8201	$10.82	$10.80	$10.80
Purchase #4	$56.49	5.460%	$59.5744	$59.57	$59.55	$59.60
Purchase #5	$214.77	5.133%	$225.7941	$225.79	$225.80	$225.80
Purchase #6	$169.80	10.138%	$187.0143	$187.01	$187.00	$187.00
Purchase #7	$174.93	6.212%	$185.7967	$185.80	$185.80	$185.80
7 purchase totals =	$952.10		$1,038.0234	$1,038.01	$1,037.95	$1,038.00