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	$7.98	11.471%	$8.8954	$8.90	$8.90	$8.90
Purchase #2	$66.28	8.706%	$72.0503	$72.05	$72.05	$72.10
Purchase #3	$69.87	12.663%	$78.7176	$78.72	$78.70	$78.70
Purchase #4	$60.85	11.132%	$67.6238	$67.62	$67.60	$67.60
Purchase #5	$166.54	10.714%	$184.3831	$184.38	$184.40	$184.40
Purchase #6	$175.95	9.542%	$192.7391	$192.74	$192.75	$192.70
Purchase #7	$72.38	12.477%	$81.4109	$81.41	$81.40	$81.40
7 purchase totals =	$619.85		$685.8202	$685.82	$685.80	$685.80