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	$83.37	7.737%	$89.8203	$89.82	$89.80	$89.80
Purchase #2	$134.31	6.555%	$143.114	$143.11	$143.10	$143.10
Purchase #3	$175.36	9.693%	$192.3576	$192.36	$192.35	$192.40
Purchase #4	$148.88	5.764%	$157.4614	$157.46	$157.45	$157.50
Purchase #5	$36.43	12.269%	$40.8996	$40.90	$40.90	$40.90
Purchase #6	$92.38	6.754%	$98.6193	$98.62	$98.60	$98.60
Purchase #7	$216.48	12.186%	$242.8603	$242.86	$242.85	$242.90
7 purchase totals =	$887.21		$965.1325	$965.13	$965.05	$965.20