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	$88.77	13.235%	$100.5187	$100.52	$100.50	$100.50
Purchase #2	$33.91	11.295%	$37.7401	$37.74	$37.75	$37.70
Purchase #3	$60.77	11.497%	$67.7567	$67.76	$67.75	$67.80
Purchase #4	$190.50	5.322%	$200.6384	$200.64	$200.65	$200.60
Purchase #5	$68.99	10.728%	$76.3912	$76.39	$76.40	$76.40
Purchase #6	$178.45	6.711%	$190.4258	$190.43	$190.45	$190.40
Purchase #7	$59.29	4.366%	$61.8786	$61.88	$61.90	$61.90
7 purchase totals =	$680.68		$735.3495	$735.36	$735.40	$735.30