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	$119.81	13.629%	$136.1389	$136.14	$136.15	$136.10
Purchase #2	$53.54	11.316%	$59.5986	$59.60	$59.60	$59.60
Purchase #3	$111.41	9.455%	$121.9438	$121.94	$121.95	$121.90
Purchase #4	$14.63	11.693%	$16.3407	$16.34	$16.35	$16.30
Purchase #5	$244.88	10.487%	$270.5606	$270.56	$270.55	$270.60
Purchase #6	$37.56	13.260%	$42.5405	$42.54	$42.55	$42.50
Purchase #7	$192.53	8.712%	$209.3032	$209.30	$209.30	$209.30
7 purchase totals =	$774.36		$856.4263	$856.42	$856.45	$856.30