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	$110.50	5.688%	$116.7852	$116.79	$116.80	$116.80
Purchase #2	$81.77	11.199%	$90.9274	$90.93	$90.95	$90.90
Purchase #3	$132.45	13.801%	$150.7294	$150.73	$150.75	$150.70
Purchase #4	$139.32	7.301%	$149.4918	$149.49	$149.50	$149.50
Purchase #5	$110.80	11.837%	$123.9154	$123.92	$123.90	$123.90
Purchase #6	$55.32	7.187%	$59.2958	$59.30	$59.30	$59.30
Purchase #7	$180.97	5.396%	$190.7351	$190.74	$190.75	$190.70
7 purchase totals =	$811.13		$881.8801	$881.90	$881.95	$881.80