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	$155.56	8.253%	$168.3984	$168.40	$168.40	$168.40
Purchase #2	$175.39	7.321%	$188.2303	$188.23	$188.25	$188.20
Purchase #3	$147.59	4.778%	$154.6419	$154.64	$154.65	$154.60
Purchase #4	$45.67	7.195%	$48.956	$48.96	$48.95	$49.00
Purchase #5	$33.27	6.571%	$35.4562	$35.46	$35.45	$35.50
Purchase #6	$94.84	10.559%	$104.8542	$104.85	$104.85	$104.90
Purchase #7	$118.27	11.475%	$131.8415	$131.84	$131.85	$131.80
7 purchase totals =	$770.59		$832.3785	$832.38	$832.40	$832.40