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	$134.27	3.863%	$139.4569	$139.46	$139.45	$139.50
Purchase #2	$82.71	8.526%	$89.7619	$89.76	$89.75	$89.80
Purchase #3	$33.78	9.310%	$36.9249	$36.92	$36.90	$36.90
Purchase #4	$227.36	7.718%	$244.9076	$244.91	$244.90	$244.90
Purchase #5	$24.45	4.840%	$25.6334	$25.63	$25.65	$25.60
Purchase #6	$24.39	13.287%	$27.6307	$27.63	$27.65	$27.60
Purchase #7	$86.81	13.141%	$98.2177	$98.22	$98.20	$98.20
7 purchase totals =	$613.77		$662.5331	$662.53	$662.50	$662.50