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	$78.99	5.248%	$83.1354	$83.14	$83.15	$83.10
Purchase #2	$37.86	6.533%	$40.3334	$40.33	$40.35	$40.30
Purchase #3	$168.41	8.346%	$182.4655	$182.47	$182.45	$182.50
Purchase #4	$241.48	6.501%	$257.1786	$257.18	$257.20	$257.20
Purchase #5	$7.63	10.530%	$8.4334	$8.43	$8.45	$8.40
Purchase #6	$140.50	10.743%	$155.5939	$155.59	$155.60	$155.60
Purchase #7	$89.58	13.199%	$101.4037	$101.40	$101.40	$101.40
7 purchase totals =	$764.45		$828.5439	$828.54	$828.60	$828.50