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	$116.95	12.193%	$131.2097	$131.21	$131.20	$131.20
Purchase #2	$127.63	7.575%	$137.298	$137.30	$137.30	$137.30
Purchase #3	$111.44	4.223%	$116.1461	$116.15	$116.15	$116.10
Purchase #4	$113.87	4.328%	$118.7983	$118.80	$118.80	$118.80
Purchase #5	$35.80	12.432%	$40.2507	$40.25	$40.25	$40.30
Purchase #6	$73.41	7.525%	$78.9341	$78.93	$78.95	$78.90
Purchase #7	$228.84	9.340%	$250.2137	$250.21	$250.20	$250.20
7 purchase totals =	$807.94		$872.8506	$872.85	$872.85	$872.80