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	$180.96	10.724%	$200.3662	$200.37	$200.35	$200.40
Purchase #2	$88.70	8.772%	$96.4808	$96.48	$96.50	$96.50
Purchase #3	$236.41	7.850%	$254.9682	$254.97	$254.95	$255.00
Purchase #4	$30.94	13.858%	$35.2277	$35.23	$35.25	$35.20
Purchase #5	$171.59	11.851%	$191.9251	$191.93	$191.95	$191.90
Purchase #6	$247.95	8.832%	$269.8489	$269.85	$269.85	$269.80
Purchase #7	$210.79	9.818%	$231.4854	$231.49	$231.50	$231.50
7 purchase totals =	$1,167.34		$1,280.3023	$1,280.32	$1,280.35	$1,280.30