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	$112.93	13.380%	$128.04	$128.04	$128.05	$128.00
Purchase #2	$37.96	7.278%	$40.7227	$40.72	$40.70	$40.70
Purchase #3	$157.94	6.234%	$167.786	$167.79	$167.80	$167.80
Purchase #4	$175.89	9.388%	$192.4026	$192.40	$192.40	$192.40
Purchase #5	$196.95	7.860%	$212.4303	$212.43	$212.45	$212.40
Purchase #6	$83.34	7.651%	$89.7163	$89.72	$89.70	$89.70
Purchase #7	$64.86	10.733%	$71.8214	$71.82	$71.80	$71.80
7 purchase totals =	$829.87		$902.9193	$902.92	$902.90	$902.80