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	$21.29	3.201%	$21.9715	$21.97	$21.95	$22.00
Purchase #2	$131.29	12.604%	$147.8378	$147.84	$147.85	$147.80
Purchase #3	$135.33	12.663%	$152.4668	$152.47	$152.45	$152.50
Purchase #4	$110.46	7.650%	$118.9102	$118.91	$118.90	$118.90
Purchase #5	$241.88	5.752%	$255.7929	$255.79	$255.80	$255.80
Purchase #6	$13.64	12.658%	$15.3666	$15.37	$15.35	$15.40
Purchase #7	$85.55	4.365%	$89.2843	$89.28	$89.30	$89.30
7 purchase totals =	$739.44		$801.6301	$801.63	$801.60	$801.70