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	$79.58	11.696%	$88.8877	$88.89	$88.90	$88.90
Purchase #2	$42.77	13.328%	$48.4704	$48.47	$48.45	$48.50
Purchase #3	$208.39	4.739%	$218.2656	$218.27	$218.25	$218.30
Purchase #4	$159.76	4.121%	$166.3437	$166.34	$166.35	$166.30
Purchase #5	$160.54	13.296%	$181.8854	$181.89	$181.90	$181.90
Purchase #6	$215.69	9.463%	$236.1007	$236.10	$236.10	$236.10
Purchase #7	$38.25	13.203%	$43.3001	$43.30	$43.30	$43.30
7 purchase totals =	$904.98		$983.2536	$983.26	$983.25	$983.30