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	$152.88	12.225%	$171.5696	$171.57	$171.55	$171.60
Purchase #2	$81.99	10.254%	$90.3973	$90.40	$90.40	$90.40
Purchase #3	$52.63	3.228%	$54.3289	$54.33	$54.35	$54.30
Purchase #4	$154.93	13.503%	$175.8502	$175.85	$175.85	$175.90
Purchase #5	$19.77	4.354%	$20.6308	$20.63	$20.65	$20.60
Purchase #6	$43.29	3.850%	$44.9567	$44.96	$44.95	$45.00
Purchase #7	$94.97	10.598%	$105.0349	$105.03	$105.05	$105.00
7 purchase totals =	$600.46		$662.7684	$662.77	$662.80	$662.80