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	$103.53	12.556%	$116.5292	$116.53	$116.55	$116.50
Purchase #2	$145.73	7.738%	$157.0066	$157.01	$157.00	$157.00
Purchase #3	$73.50	7.103%	$78.7207	$78.72	$78.70	$78.70
Purchase #4	$43.94	11.404%	$48.9509	$48.95	$48.95	$49.00
Purchase #5	$136.80	7.643%	$147.2556	$147.26	$147.25	$147.30
Purchase #6	$103.86	10.856%	$115.135	$115.14	$115.15	$115.10
Purchase #7	$152.49	6.849%	$162.934	$162.93	$162.95	$162.90
7 purchase totals =	$759.85		$826.5320	$826.54	$826.55	$826.50