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	$113.34	5.516%	$119.5918	$119.59	$119.60	$119.60
Purchase #2	$126.45	7.720%	$136.2119	$136.21	$136.20	$136.20
Purchase #3	$161.40	4.607%	$168.8357	$168.84	$168.85	$168.80
Purchase #4	$91.55	13.740%	$104.129	$104.13	$104.15	$104.10
Purchase #5	$77.61	3.671%	$80.4591	$80.46	$80.45	$80.50
Purchase #6	$79.53	3.610%	$82.401	$82.40	$82.40	$82.40
Purchase #7	$44.39	9.173%	$48.4619	$48.46	$48.45	$48.50
7 purchase totals =	$694.27		$740.0904	$740.09	$740.10	$740.10