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	$53.87	12.136%	$60.4077	$60.41	$60.40	$60.40
Purchase #2	$187.79	13.368%	$212.8938	$212.89	$212.90	$212.90
Purchase #3	$33.49	8.646%	$36.3855	$36.39	$36.40	$36.40
Purchase #4	$182.38	3.800%	$189.3104	$189.31	$189.30	$189.30
Purchase #5	$46.58	8.167%	$50.3842	$50.38	$50.40	$50.40
Purchase #6	$71.72	12.861%	$80.9439	$80.94	$80.95	$80.90
Purchase #7	$41.60	9.587%	$45.5882	$45.59	$45.60	$45.60
7 purchase totals =	$617.43		$675.9137	$675.91	$675.95	$675.90