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	$10.27	5.374%	$10.8219	$10.82	$10.80	$10.80
Purchase #2	$210.89	13.869%	$240.1383	$240.14	$240.15	$240.10
Purchase #3	$133.78	7.317%	$143.5687	$143.57	$143.55	$143.60
Purchase #4	$133.50	4.499%	$139.5062	$139.51	$139.50	$139.50
Purchase #5	$232.86	9.474%	$254.9212	$254.92	$254.90	$254.90
Purchase #6	$174.28	6.712%	$185.9777	$185.98	$186.00	$186.00
Purchase #7	$106.26	4.203%	$110.7261	$110.73	$110.75	$110.70
7 purchase totals =	$1,001.84		$1,085.6601	$1,085.67	$1,085.65	$1,085.60