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	$37.41	10.638%	$41.3897	$41.39	$41.40	$41.40
Purchase #2	$200.78	7.416%	$215.6698	$215.67	$215.65	$215.70
Purchase #3	$117.88	11.575%	$131.5246	$131.52	$131.50	$131.50
Purchase #4	$205.69	7.146%	$220.3886	$220.39	$220.40	$220.40
Purchase #5	$53.26	8.111%	$57.5799	$57.58	$57.60	$57.60
Purchase #6	$7.35	5.136%	$7.7275	$7.73	$7.75	$7.70
Purchase #7	$216.96	12.739%	$244.5985	$244.60	$244.60	$244.60
7 purchase totals =	$839.33		$918.8786	$918.88	$918.90	$918.90