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	$221.32	7.237%	$237.3369	$237.34	$237.35	$237.30
Purchase #2	$115.81	6.553%	$123.399	$123.40	$123.40	$123.40
Purchase #3	$116.92	5.276%	$123.0887	$123.09	$123.10	$123.10
Purchase #4	$38.63	9.630%	$42.3501	$42.35	$42.35	$42.40
Purchase #5	$97.84	13.794%	$111.336	$111.34	$111.35	$111.30
Purchase #6	$26.36	6.283%	$28.0162	$28.02	$28.00	$28.00
Purchase #7	$237.84	11.467%	$265.1131	$265.11	$265.10	$265.10
7 purchase totals =	$854.72		$930.6400	$930.65	$930.65	$930.60