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	$76.57	6.831%	$81.8005	$81.80	$81.80	$81.80
Purchase #2	$76.33	6.465%	$81.2647	$81.26	$81.25	$81.30
Purchase #3	$155.37	10.292%	$171.3607	$171.36	$171.35	$171.40
Purchase #4	$70.50	11.293%	$78.4616	$78.46	$78.45	$78.50
Purchase #5	$235.46	5.809%	$249.1379	$249.14	$249.15	$249.10
Purchase #6	$139.92	3.220%	$144.4254	$144.43	$144.45	$144.40
Purchase #7	$106.67	4.108%	$111.052	$111.05	$111.05	$111.10
7 purchase totals =	$860.82		$917.5028	$917.50	$917.50	$917.60