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	$92.81	7.253%	$99.5415	$99.54	$99.55	$99.50
Purchase #2	$40.44	8.607%	$43.9207	$43.92	$43.90	$43.90
Purchase #3	$123.32	7.281%	$132.2989	$132.30	$132.30	$132.30
Purchase #4	$59.43	6.591%	$63.347	$63.35	$63.35	$63.30
Purchase #5	$78.73	12.328%	$88.4358	$88.44	$88.45	$88.40
Purchase #6	$220.80	10.776%	$244.5934	$244.59	$244.60	$244.60
Purchase #7	$164.54	13.541%	$186.8204	$186.82	$186.80	$186.80
7 purchase totals =	$780.07		$858.9577	$858.96	$858.95	$858.80