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	$109.64	6.508%	$116.7754	$116.78	$116.80	$116.80
Purchase #2	$125.61	12.649%	$141.4984	$141.50	$141.50	$141.50
Purchase #3	$23.38	13.170%	$26.4591	$26.46	$26.45	$26.50
Purchase #4	$78.42	12.644%	$88.3354	$88.34	$88.35	$88.30
Purchase #5	$81.40	11.693%	$90.9181	$90.92	$90.90	$90.90
Purchase #6	$19.46	10.275%	$21.4595	$21.46	$21.45	$21.50
Purchase #7	$38.27	11.790%	$42.782	$42.78	$42.80	$42.80
7 purchase totals =	$476.18		$528.2279	$528.24	$528.25	$528.30