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	$125.64	13.579%	$142.7007	$142.70	$142.70	$142.70
Purchase #2	$102.41	9.296%	$111.93	$111.93	$111.95	$111.90
Purchase #3	$65.99	11.452%	$73.5472	$73.55	$73.55	$73.50
Purchase #4	$215.89	11.428%	$240.5619	$240.56	$240.55	$240.60
Purchase #5	$40.91	4.825%	$42.8839	$42.88	$42.90	$42.90
Purchase #6	$96.25	11.651%	$107.4641	$107.46	$107.45	$107.50
Purchase #7	$77.95	9.488%	$85.3459	$85.35	$85.35	$85.30
7 purchase totals =	$725.04		$804.4337	$804.43	$804.45	$804.40