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	$184.38	13.727%	$209.6898	$209.69	$209.70	$209.70
Purchase #2	$36.39	6.843%	$38.8802	$38.88	$38.90	$38.90
Purchase #3	$12.56	9.704%	$13.7788	$13.78	$13.80	$13.80
Purchase #4	$76.71	5.737%	$81.1109	$81.11	$81.10	$81.10
Purchase #5	$105.47	4.156%	$109.8533	$109.85	$109.85	$109.90
Purchase #6	$242.55	12.784%	$273.5576	$273.56	$273.55	$273.60
Purchase #7	$76.71	7.295%	$82.306	$82.31	$82.30	$82.30
7 purchase totals =	$734.77		$809.1766	$809.18	$809.20	$809.30