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	$142.96	10.342%	$157.7449	$157.74	$157.75	$157.70
Purchase #2	$123.31	5.771%	$130.4262	$130.43	$130.45	$130.40
Purchase #3	$12.46	11.579%	$13.9027	$13.90	$13.90	$13.90
Purchase #4	$43.47	5.548%	$45.8817	$45.88	$45.90	$45.90
Purchase #5	$240.39	7.641%	$258.7582	$258.76	$258.75	$258.80
Purchase #6	$198.64	5.507%	$209.5791	$209.58	$209.60	$209.60
Purchase #7	$129.55	7.758%	$139.6005	$139.60	$139.60	$139.60
7 purchase totals =	$890.78		$955.8933	$955.89	$955.95	$955.90