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	$78.35	12.853%	$88.4203	$88.42	$88.40	$88.40
Purchase #2	$109.95	11.238%	$122.3062	$122.31	$122.30	$122.30
Purchase #3	$134.92	5.600%	$142.4755	$142.48	$142.50	$142.50
Purchase #4	$30.56	7.338%	$32.8025	$32.80	$32.80	$32.80
Purchase #5	$114.30	3.615%	$118.4319	$118.43	$118.45	$118.40
Purchase #6	$33.52	11.330%	$37.3178	$37.32	$37.30	$37.30
Purchase #7	$225.89	7.441%	$242.6985	$242.70	$242.70	$242.70
7 purchase totals =	$727.49		$784.4527	$784.46	$784.45	$784.40