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	$244.33	13.688%	$277.7739	$277.77	$277.75	$277.80
Purchase #2	$37.60	13.669%	$42.7395	$42.74	$42.75	$42.70
Purchase #3	$21.71	13.619%	$24.6667	$24.67	$24.65	$24.70
Purchase #4	$80.33	8.800%	$87.399	$87.40	$87.40	$87.40
Purchase #5	$37.44	12.734%	$42.2076	$42.21	$42.20	$42.20
Purchase #6	$140.63	3.175%	$145.095	$145.10	$145.10	$145.10
Purchase #7	$64.34	12.751%	$72.544	$72.54	$72.55	$72.50
7 purchase totals =	$626.38		$692.4257	$692.43	$692.40	$692.40