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	$60.30	10.419%	$66.5827	$66.58	$66.60	$66.60
Purchase #2	$13.90	5.279%	$14.6338	$14.63	$14.65	$14.60
Purchase #3	$243.44	7.644%	$262.0486	$262.05	$262.05	$262.00
Purchase #4	$32.89	7.583%	$35.384	$35.38	$35.40	$35.40
Purchase #5	$5.60	11.589%	$6.249	$6.25	$6.25	$6.20
Purchase #6	$222.93	12.505%	$250.8074	$250.81	$250.80	$250.80
Purchase #7	$67.40	5.134%	$70.8603	$70.86	$70.85	$70.90
7 purchase totals =	$646.46		$706.5658	$706.56	$706.60	$706.50