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	$13.71	13.673%	$15.5846	$15.58	$15.60	$15.60
Purchase #2	$81.88	10.382%	$90.3808	$90.38	$90.40	$90.40
Purchase #3	$85.96	12.742%	$96.913	$96.91	$96.90	$96.90
Purchase #4	$236.65	7.306%	$253.9396	$253.94	$253.95	$253.90
Purchase #5	$72.55	10.522%	$80.1837	$80.18	$80.20	$80.20
Purchase #6	$180.74	6.189%	$191.926	$191.93	$191.95	$191.90
Purchase #7	$30.61	9.575%	$33.5409	$33.54	$33.55	$33.50
7 purchase totals =	$702.10		$762.4686	$762.46	$762.55	$762.40