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	$157.57	5.727%	$166.594	$166.59	$166.60	$166.60
Purchase #2	$37.54	7.104%	$40.2068	$40.21	$40.20	$40.20
Purchase #3	$53.72	4.578%	$56.1793	$56.18	$56.20	$56.20
Purchase #4	$39.47	9.841%	$43.3542	$43.35	$43.35	$43.40
Purchase #5	$202.73	11.172%	$225.379	$225.38	$225.40	$225.40
Purchase #6	$190.88	9.349%	$208.7254	$208.73	$208.75	$208.70
Purchase #7	$85.29	6.602%	$90.9208	$90.92	$90.90	$90.90
7 purchase totals =	$767.20		$831.3595	$831.36	$831.40	$831.40