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	$26.43	5.550%	$27.8969	$27.90	$27.90	$27.90
Purchase #2	$119.31	8.493%	$129.443	$129.44	$129.45	$129.40
Purchase #3	$52.31	13.652%	$59.4514	$59.45	$59.45	$59.50
Purchase #4	$131.53	7.664%	$141.6105	$141.61	$141.60	$141.60
Purchase #5	$234.56	11.561%	$261.6775	$261.68	$261.70	$261.70
Purchase #6	$36.48	11.257%	$40.5866	$40.59	$40.60	$40.60
Purchase #7	$224.87	4.592%	$235.196	$235.20	$235.20	$235.20
7 purchase totals =	$825.49		$895.8619	$895.87	$895.90	$895.90