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	$179.38	5.706%	$189.6154	$189.62	$189.60	$189.60
Purchase #2	$82.48	9.836%	$90.5927	$90.59	$90.60	$90.60
Purchase #3	$231.47	5.140%	$243.3676	$243.37	$243.35	$243.40
Purchase #4	$32.33	12.157%	$36.2604	$36.26	$36.25	$36.30
Purchase #5	$43.40	3.633%	$44.9767	$44.98	$45.00	$45.00
Purchase #6	$54.55	10.355%	$60.1987	$60.20	$60.20	$60.20
Purchase #7	$37.52	8.223%	$40.6053	$40.61	$40.60	$40.60
7 purchase totals =	$661.13		$705.6168	$705.63	$705.60	$705.70