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	$37.73	11.745%	$42.1614	$42.16	$42.15	$42.20
Purchase #2	$120.75	12.747%	$136.142	$136.14	$136.15	$136.10
Purchase #3	$80.80	6.570%	$86.1086	$86.11	$86.10	$86.10
Purchase #4	$88.98	3.468%	$92.0658	$92.07	$92.05	$92.10
Purchase #5	$134.77	3.490%	$139.4735	$139.47	$139.45	$139.50
Purchase #6	$143.38	13.284%	$162.4266	$162.43	$162.45	$162.40
Purchase #7	$143.40	3.262%	$148.0777	$148.08	$148.10	$148.10
7 purchase totals =	$749.81		$806.4556	$806.46	$806.45	$806.50