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	$31.82	10.494%	$35.1592	$35.16	$35.15	$35.20
Purchase #2	$50.56	11.838%	$56.5453	$56.55	$56.55	$56.50
Purchase #3	$212.27	5.612%	$224.1826	$224.18	$224.20	$224.20
Purchase #4	$109.81	12.453%	$123.4846	$123.48	$123.50	$123.50
Purchase #5	$99.89	11.639%	$111.5162	$111.52	$111.50	$111.50
Purchase #6	$94.75	3.740%	$98.2937	$98.29	$98.30	$98.30
Purchase #7	$109.47	5.587%	$115.5861	$115.59	$115.60	$115.60
7 purchase totals =	$708.57		$764.7677	$764.77	$764.80	$764.80