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	$65.98	4.279%	$68.8033	$68.80	$68.80	$68.80
Purchase #2	$72.89	6.650%	$77.7372	$77.74	$77.75	$77.70
Purchase #3	$176.43	5.417%	$185.9872	$185.99	$186.00	$186.00
Purchase #4	$153.99	3.431%	$159.2734	$159.27	$159.25	$159.30
Purchase #5	$181.60	10.194%	$200.1123	$200.11	$200.10	$200.10
Purchase #6	$215.33	12.641%	$242.5499	$242.55	$242.55	$242.50
Purchase #7	$64.85	4.621%	$67.8467	$67.85	$67.85	$67.80
7 purchase totals =	$931.07		$1,002.3100	$1,002.31	$1,002.30	$1,002.20