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	$73.49	6.595%	$78.3367	$78.34	$78.35	$78.30
Purchase #2	$147.82	12.355%	$166.0832	$166.08	$166.10	$166.10
Purchase #3	$67.34	6.295%	$71.5791	$71.58	$71.60	$71.60
Purchase #4	$186.33	3.348%	$192.5683	$192.57	$192.55	$192.60
Purchase #5	$152.37	7.493%	$163.7871	$163.79	$163.80	$163.80
Purchase #6	$106.37	4.400%	$111.0503	$111.05	$111.05	$111.10
Purchase #7	$90.69	8.851%	$98.717	$98.72	$98.70	$98.70
7 purchase totals =	$824.41		$882.1217	$882.13	$882.15	$882.20