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	$153.45	11.495%	$171.0891	$171.09	$171.10	$171.10
Purchase #2	$35.99	12.705%	$40.5625	$40.56	$40.55	$40.60
Purchase #3	$125.78	12.778%	$141.8522	$141.85	$141.85	$141.90
Purchase #4	$116.56	4.152%	$121.3996	$121.40	$121.40	$121.40
Purchase #5	$75.45	3.874%	$78.3729	$78.37	$78.35	$78.40
Purchase #6	$245.54	6.546%	$261.613	$261.61	$261.60	$261.60
Purchase #7	$79.86	6.725%	$85.2306	$85.23	$85.25	$85.20
7 purchase totals =	$832.63		$900.1199	$900.11	$900.10	$900.20