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	$112.49	9.424%	$123.0911	$123.09	$123.10	$123.10
Purchase #2	$87.39	3.617%	$90.5509	$90.55	$90.55	$90.60
Purchase #3	$232.96	8.207%	$252.079	$252.08	$252.10	$252.10
Purchase #4	$31.30	13.116%	$35.4053	$35.41	$35.40	$35.40
Purchase #5	$180.31	5.431%	$190.1026	$190.10	$190.10	$190.10
Purchase #6	$175.78	13.340%	$199.2291	$199.23	$199.25	$199.20
Purchase #7	$99.46	6.701%	$106.1248	$106.12	$106.10	$106.10
7 purchase totals =	$919.69		$996.5828	$996.58	$996.60	$996.60