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	$111.78	6.185%	$118.6936	$118.69	$118.70	$118.70
Purchase #2	$223.57	12.328%	$251.1317	$251.13	$251.15	$251.10
Purchase #3	$198.88	5.755%	$210.3255	$210.33	$210.35	$210.30
Purchase #4	$181.50	10.678%	$200.8806	$200.88	$200.90	$200.90
Purchase #5	$250.62	12.828%	$282.7695	$282.77	$282.75	$282.80
Purchase #6	$247.51	13.200%	$280.1813	$280.18	$280.20	$280.20
Purchase #7	$177.83	7.845%	$191.7808	$191.78	$191.80	$191.80
7 purchase totals =	$1,391.69		$1,535.7630	$1,535.76	$1,535.85	$1,535.80