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	$247.36	13.549%	$280.8748	$280.87	$280.85	$280.90
Purchase #2	$122.96	11.753%	$137.4115	$137.41	$137.40	$137.40
Purchase #3	$71.57	12.850%	$80.7667	$80.77	$80.75	$80.80
Purchase #4	$104.54	12.380%	$117.4821	$117.48	$117.50	$117.50
Purchase #5	$216.56	8.465%	$234.8918	$234.89	$234.90	$234.90
Purchase #6	$96.70	4.780%	$101.3223	$101.32	$101.30	$101.30
Purchase #7	$239.32	7.328%	$256.8574	$256.86	$256.85	$256.90
7 purchase totals =	$1,099.01		$1,209.6066	$1,209.60	$1,209.55	$1,209.70