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	$69.60	12.503%	$78.3021	$78.30	$78.30	$78.30
Purchase #2	$113.86	8.357%	$123.3753	$123.38	$123.40	$123.40
Purchase #3	$32.50	5.544%	$34.3018	$34.30	$34.30	$34.30
Purchase #4	$195.44	12.188%	$219.2602	$219.26	$219.25	$219.30
Purchase #5	$197.41	13.220%	$223.5076	$223.51	$223.50	$223.50
Purchase #6	$72.56	7.705%	$78.1507	$78.15	$78.15	$78.20
Purchase #7	$100.31	10.808%	$111.1515	$111.15	$111.15	$111.20
7 purchase totals =	$781.68		$868.0492	$868.05	$868.05	$868.20