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	$16.93	11.388%	$18.858	$18.86	$18.85	$18.90
Purchase #2	$62.42	13.250%	$70.6907	$70.69	$70.70	$70.70
Purchase #3	$33.41	11.600%	$37.2856	$37.29	$37.30	$37.30
Purchase #4	$200.70	4.661%	$210.0546	$210.05	$210.05	$210.10
Purchase #5	$218.81	12.239%	$245.5902	$245.59	$245.60	$245.60
Purchase #6	$154.59	7.392%	$166.0173	$166.02	$166.00	$166.00
Purchase #7	$104.91	3.774%	$108.8693	$108.87	$108.85	$108.90
7 purchase totals =	$791.77		$857.3657	$857.37	$857.35	$857.50