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	$67.55	6.418%	$71.8854	$71.89	$71.90	$71.90
Purchase #2	$30.60	8.782%	$33.2873	$33.29	$33.30	$33.30
Purchase #3	$220.47	5.290%	$232.1329	$232.13	$232.15	$232.10
Purchase #4	$190.26	12.768%	$214.5524	$214.55	$214.55	$214.60
Purchase #5	$119.57	9.751%	$131.2293	$131.23	$131.25	$131.20
Purchase #6	$97.79	7.660%	$105.2807	$105.28	$105.30	$105.30
Purchase #7	$16.25	11.448%	$18.1103	$18.11	$18.10	$18.10
7 purchase totals =	$742.49		$806.4783	$806.48	$806.55	$806.50