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	$220.71	13.336%	$250.1439	$250.14	$250.15	$250.10
Purchase #2	$59.86	4.180%	$62.3621	$62.36	$62.35	$62.40
Purchase #3	$31.85	12.299%	$35.7672	$35.77	$35.75	$35.80
Purchase #4	$166.50	11.275%	$185.2729	$185.27	$185.25	$185.30
Purchase #5	$95.97	11.643%	$107.1438	$107.14	$107.15	$107.10
Purchase #6	$23.68	7.736%	$25.5119	$25.51	$25.50	$25.50
Purchase #7	$215.94	6.110%	$229.1339	$229.13	$229.15	$229.10
7 purchase totals =	$814.51		$895.3357	$895.32	$895.30	$895.30