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	$93.99	6.830%	$100.4095	$100.41	$100.40	$100.40
Purchase #2	$50.68	10.273%	$55.8864	$55.89	$55.90	$55.90
Purchase #3	$216.89	11.788%	$242.457	$242.46	$242.45	$242.50
Purchase #4	$222.30	12.167%	$249.3472	$249.35	$249.35	$249.30
Purchase #5	$62.47	7.318%	$67.0416	$67.04	$67.05	$67.00
Purchase #6	$241.40	12.109%	$270.6311	$270.63	$270.65	$270.60
Purchase #7	$28.89	11.408%	$32.1858	$32.19	$32.20	$32.20
7 purchase totals =	$916.62		$1,017.9586	$1,017.97	$1,018.00	$1,017.90