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	$38.96	3.647%	$40.3809	$40.38	$40.40	$40.40
Purchase #2	$59.91	11.696%	$66.9171	$66.92	$66.90	$66.90
Purchase #3	$77.48	8.112%	$83.7652	$83.77	$83.75	$83.80
Purchase #4	$96.67	9.166%	$105.5308	$105.53	$105.55	$105.50
Purchase #5	$176.32	13.112%	$199.4391	$199.44	$199.45	$199.40
Purchase #6	$13.89	12.607%	$15.6411	$15.64	$15.65	$15.60
Purchase #7	$33.99	8.155%	$36.7619	$36.76	$36.75	$36.80
7 purchase totals =	$497.22		$548.4361	$548.44	$548.45	$548.40