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	$39.50	9.864%	$43.3963	$43.40	$43.40	$43.40
Purchase #2	$206.32	10.377%	$227.7298	$227.73	$227.75	$227.70
Purchase #3	$120.37	6.497%	$128.1904	$128.19	$128.20	$128.20
Purchase #4	$150.48	10.431%	$166.1766	$166.18	$166.20	$166.20
Purchase #5	$139.36	9.226%	$152.2174	$152.22	$152.20	$152.20
Purchase #6	$235.30	8.330%	$254.9005	$254.90	$254.90	$254.90
Purchase #7	$73.60	12.703%	$82.9494	$82.95	$82.95	$82.90
7 purchase totals =	$964.93		$1,055.5604	$1,055.57	$1,055.60	$1,055.50