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	$86.88	3.130%	$89.5993	$89.60	$89.60	$89.60
Purchase #2	$207.42	4.355%	$216.4531	$216.45	$216.45	$216.50
Purchase #3	$143.31	8.790%	$155.9069	$155.91	$155.90	$155.90
Purchase #4	$41.50	12.239%	$46.5792	$46.58	$46.60	$46.60
Purchase #5	$189.59	12.597%	$213.4727	$213.47	$213.45	$213.50
Purchase #6	$230.70	3.536%	$238.8576	$238.86	$238.85	$238.90
Purchase #7	$171.39	11.487%	$191.0776	$191.08	$191.10	$191.10
7 purchase totals =	$1,070.79		$1,151.9464	$1,151.95	$1,151.95	$1,152.10