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	$53.80	11.512%	$59.9935	$59.99	$60.00	$60.00
Purchase #2	$147.33	6.296%	$156.6059	$156.61	$156.60	$156.60
Purchase #3	$109.96	9.438%	$120.338	$120.34	$120.35	$120.30
Purchase #4	$45.65	3.409%	$47.2062	$47.21	$47.20	$47.20
Purchase #5	$72.37	8.833%	$78.7624	$78.76	$78.75	$78.80
Purchase #6	$235.82	12.162%	$264.5004	$264.50	$264.50	$264.50
Purchase #7	$107.51	4.628%	$112.4856	$112.49	$112.50	$112.50
7 purchase totals =	$772.44		$839.8920	$839.90	$839.90	$839.90