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	$80.31	11.791%	$89.7794	$89.78	$89.80	$89.80
Purchase #2	$209.84	4.185%	$218.6218	$218.62	$218.60	$218.60
Purchase #3	$246.53	11.555%	$275.0165	$275.02	$275.00	$275.00
Purchase #4	$78.57	5.727%	$83.0697	$83.07	$83.05	$83.10
Purchase #5	$229.36	4.125%	$238.8211	$238.82	$238.80	$238.80
Purchase #6	$218.64	7.821%	$235.7398	$235.74	$235.75	$235.70
Purchase #7	$249.93	3.296%	$258.1677	$258.17	$258.15	$258.20
7 purchase totals =	$1,313.18		$1,399.2160	$1,399.22	$1,399.15	$1,399.20