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	$242.59	7.741%	$261.3689	$261.37	$261.35	$261.40
Purchase #2	$248.36	10.284%	$273.9013	$273.90	$273.90	$273.90
Purchase #3	$246.63	13.524%	$279.9842	$279.98	$280.00	$280.00
Purchase #4	$236.57	5.372%	$249.2785	$249.28	$249.30	$249.30
Purchase #5	$142.81	12.588%	$160.7869	$160.79	$160.80	$160.80
Purchase #6	$66.55	9.440%	$72.8323	$72.83	$72.85	$72.80
Purchase #7	$25.38	11.356%	$28.2622	$28.26	$28.25	$28.30
7 purchase totals =	$1,208.89		$1,326.4143	$1,326.41	$1,326.45	$1,326.50