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	$5.28	11.722%	$5.8989	$5.90	$5.90	$5.90
Purchase #2	$50.76	7.158%	$54.3934	$54.39	$54.40	$54.40
Purchase #3	$250.51	11.765%	$279.9825	$279.98	$280.00	$280.00
Purchase #4	$211.28	11.393%	$235.3511	$235.35	$235.35	$235.40
Purchase #5	$174.48	4.830%	$182.9074	$182.91	$182.90	$182.90
Purchase #6	$103.31	12.714%	$116.4448	$116.44	$116.45	$116.40
Purchase #7	$160.42	13.729%	$182.4441	$182.44	$182.45	$182.40
7 purchase totals =	$956.04		$1,057.4222	$1,057.41	$1,057.45	$1,057.40