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	$83.77	6.517%	$89.2293	$89.23	$89.25	$89.20
Purchase #2	$154.71	4.108%	$161.0655	$161.07	$161.05	$161.10
Purchase #3	$127.56	12.272%	$143.2142	$143.21	$143.20	$143.20
Purchase #4	$154.30	10.227%	$170.0803	$170.08	$170.10	$170.10
Purchase #5	$127.91	7.404%	$137.3805	$137.38	$137.40	$137.40
Purchase #6	$220.89	4.804%	$231.5016	$231.50	$231.50	$231.50
Purchase #7	$7.96	11.344%	$8.863	$8.86	$8.85	$8.90
7 purchase totals =	$877.10		$941.3344	$941.33	$941.35	$941.40