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	$136.79	9.810%	$150.2091	$150.21	$150.20	$150.20
Purchase #2	$30.79	6.454%	$32.7772	$32.78	$32.80	$32.80
Purchase #3	$63.57	6.125%	$67.4637	$67.46	$67.45	$67.50
Purchase #4	$48.90	11.495%	$54.5211	$54.52	$54.50	$54.50
Purchase #5	$247.47	13.249%	$280.2573	$280.26	$280.25	$280.30
Purchase #6	$184.68	8.463%	$200.3095	$200.31	$200.30	$200.30
Purchase #7	$30.91	3.118%	$31.8738	$31.87	$31.85	$31.90
7 purchase totals =	$743.11		$817.4117	$817.41	$817.35	$817.50