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	$240.84	13.673%	$273.7701	$273.77	$273.75	$273.80
Purchase #2	$114.84	8.433%	$124.5245	$124.52	$124.50	$124.50
Purchase #3	$50.27	8.408%	$54.4967	$54.50	$54.50	$54.50
Purchase #4	$167.91	7.128%	$179.8786	$179.88	$179.90	$179.90
Purchase #5	$180.49	4.683%	$188.9423	$188.94	$188.95	$188.90
Purchase #6	$77.56	11.317%	$86.3375	$86.34	$86.35	$86.30
Purchase #7	$45.92	12.801%	$51.7982	$51.80	$51.80	$51.80
7 purchase totals =	$877.83		$959.7479	$959.75	$959.75	$959.70