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	$90.78	6.388%	$96.579	$96.58	$96.60	$96.60
Purchase #2	$6.88	8.727%	$7.4804	$7.48	$7.50	$7.50
Purchase #3	$208.84	4.848%	$218.9646	$218.96	$218.95	$219.00
Purchase #4	$133.90	9.646%	$146.816	$146.82	$146.80	$146.80
Purchase #5	$31.97	11.153%	$35.5356	$35.54	$35.55	$35.50
Purchase #6	$46.51	10.684%	$51.4791	$51.48	$51.50	$51.50
Purchase #7	$239.77	13.268%	$271.5827	$271.58	$271.60	$271.60
7 purchase totals =	$758.65		$828.4374	$828.44	$828.50	$828.50