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	$157.77	8.853%	$171.7374	$171.74	$171.75	$171.70
Purchase #2	$13.44	7.466%	$14.4434	$14.44	$14.45	$14.40
Purchase #3	$196.54	13.534%	$223.1397	$223.14	$223.15	$223.10
Purchase #4	$161.86	5.650%	$171.0051	$171.01	$171.00	$171.00
Purchase #5	$36.49	5.759%	$38.5915	$38.59	$38.60	$38.60
Purchase #6	$70.70	13.405%	$80.1773	$80.18	$80.20	$80.20
Purchase #7	$63.39	12.834%	$71.5255	$71.53	$71.55	$71.50
7 purchase totals =	$700.19		$770.6199	$770.63	$770.70	$770.50