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	$64.86	13.113%	$73.3651	$73.37	$73.35	$73.40
Purchase #2	$104.71	13.304%	$118.6406	$118.64	$118.65	$118.60
Purchase #3	$114.54	12.155%	$128.4623	$128.46	$128.45	$128.50
Purchase #4	$137.29	9.503%	$150.3367	$150.34	$150.35	$150.30
Purchase #5	$238.36	9.620%	$261.2902	$261.29	$261.30	$261.30
Purchase #6	$101.89	12.233%	$114.3542	$114.35	$114.35	$114.40
Purchase #7	$83.86	7.293%	$89.9759	$89.98	$90.00	$90.00
7 purchase totals =	$845.51		$936.4250	$936.43	$936.45	$936.50