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	$250.81	11.753%	$280.2877	$280.29	$280.30	$280.30
Purchase #2	$145.77	9.145%	$159.1007	$159.10	$159.10	$159.10
Purchase #3	$153.93	10.810%	$170.5698	$170.57	$170.55	$170.60
Purchase #4	$29.34	13.129%	$33.192	$33.19	$33.20	$33.20
Purchase #5	$171.56	10.483%	$189.5446	$189.54	$189.55	$189.50
Purchase #6	$114.85	7.449%	$123.4052	$123.41	$123.40	$123.40
Purchase #7	$72.45	12.240%	$81.3179	$81.32	$81.30	$81.30
7 purchase totals =	$938.71		$1,037.4179	$1,037.42	$1,037.40	$1,037.40