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	$48.85	13.207%	$55.3016	$55.30	$55.30	$55.30
Purchase #2	$35.93	3.490%	$37.184	$37.18	$37.20	$37.20
Purchase #3	$194.41	7.131%	$208.2734	$208.27	$208.25	$208.30
Purchase #4	$46.61	5.855%	$49.339	$49.34	$49.35	$49.30
Purchase #5	$167.85	6.261%	$178.3591	$178.36	$178.35	$178.40
Purchase #6	$137.81	6.601%	$146.9068	$146.91	$146.90	$146.90
Purchase #7	$148.90	12.761%	$167.9011	$167.90	$167.90	$167.90
7 purchase totals =	$780.36		$843.2650	$843.26	$843.25	$843.30