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	$126.59	7.863%	$136.5438	$136.54	$136.55	$136.50
Purchase #2	$228.51	3.676%	$236.91	$236.91	$236.90	$236.90
Purchase #3	$125.58	10.110%	$138.2761	$138.28	$138.30	$138.30
Purchase #4	$208.37	10.819%	$230.9136	$230.91	$230.90	$230.90
Purchase #5	$91.63	13.280%	$103.7985	$103.80	$103.80	$103.80
Purchase #6	$152.53	12.513%	$171.6161	$171.62	$171.60	$171.60
Purchase #7	$52.77	13.327%	$59.8027	$59.80	$59.80	$59.80
7 purchase totals =	$985.98		$1,077.8608	$1,077.86	$1,077.85	$1,077.80