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	$129.97	7.161%	$139.2772	$139.28	$139.30	$139.30
Purchase #2	$168.82	6.757%	$180.2272	$180.23	$180.25	$180.20
Purchase #3	$179.39	13.825%	$204.1907	$204.19	$204.20	$204.20
Purchase #4	$100.87	9.669%	$110.6231	$110.62	$110.60	$110.60
Purchase #5	$73.31	6.392%	$77.996	$78.00	$78.00	$78.00
Purchase #6	$198.79	12.870%	$224.3743	$224.37	$224.35	$224.40
Purchase #7	$149.28	13.146%	$168.9043	$168.90	$168.90	$168.90
7 purchase totals =	$1,000.43		$1,105.5928	$1,105.59	$1,105.60	$1,105.60