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	$203.70	7.209%	$218.3847	$218.38	$218.40	$218.40
Purchase #2	$71.89	11.157%	$79.9108	$79.91	$79.90	$79.90
Purchase #3	$147.86	5.575%	$156.1032	$156.10	$156.10	$156.10
Purchase #4	$116.55	13.556%	$132.3495	$132.35	$132.35	$132.30
Purchase #5	$18.59	13.631%	$21.124	$21.12	$21.10	$21.10
Purchase #6	$242.73	4.403%	$253.4174	$253.42	$253.40	$253.40
Purchase #7	$35.38	6.771%	$37.7756	$37.78	$37.80	$37.80
7 purchase totals =	$836.70		$899.0652	$899.06	$899.05	$899.00