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	$42.34	4.502%	$44.2461	$44.25	$44.25	$44.20
Purchase #2	$33.66	13.319%	$38.1432	$38.14	$38.15	$38.10
Purchase #3	$108.78	9.686%	$119.3164	$119.32	$119.30	$119.30
Purchase #4	$168.66	12.787%	$190.2266	$190.23	$190.25	$190.20
Purchase #5	$31.38	10.304%	$34.6134	$34.61	$34.60	$34.60
Purchase #6	$16.50	9.853%	$18.1257	$18.13	$18.15	$18.10
Purchase #7	$85.65	11.481%	$95.4835	$95.48	$95.50	$95.50
7 purchase totals =	$486.97		$540.1549	$540.16	$540.20	$540.00