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	$250.45	7.872%	$270.1654	$270.17	$270.15	$270.20
Purchase #2	$107.51	4.817%	$112.6888	$112.69	$112.70	$112.70
Purchase #3	$123.75	9.400%	$135.3825	$135.38	$135.40	$135.40
Purchase #4	$40.33	4.544%	$42.1626	$42.16	$42.15	$42.20
Purchase #5	$217.50	10.582%	$240.5159	$240.52	$240.50	$240.50
Purchase #6	$34.52	7.541%	$37.1232	$37.12	$37.10	$37.10
Purchase #7	$201.67	4.584%	$210.9146	$210.91	$210.90	$210.90
7 purchase totals =	$975.73		$1,048.9530	$1,048.95	$1,048.90	$1,049.00