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	$240.63	13.771%	$273.7672	$273.77	$273.75	$273.80
Purchase #2	$162.87	11.596%	$181.7564	$181.76	$181.75	$181.80
Purchase #3	$247.26	13.263%	$280.0541	$280.05	$280.05	$280.10
Purchase #4	$181.76	10.120%	$200.1541	$200.15	$200.15	$200.20
Purchase #5	$168.89	13.619%	$191.8911	$191.89	$191.90	$191.90
Purchase #6	$87.35	4.869%	$91.6031	$91.60	$91.60	$91.60
Purchase #7	$26.76	3.467%	$27.6878	$27.69	$27.70	$27.70
7 purchase totals =	$1,115.52		$1,246.9138	$1,246.91	$1,246.90	$1,247.10