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	$82.45	9.326%	$90.1393	$90.14	$90.15	$90.10
Purchase #2	$93.96	10.623%	$103.9414	$103.94	$103.95	$103.90
Purchase #3	$209.88	12.858%	$236.8664	$236.87	$236.85	$236.90
Purchase #4	$208.30	6.371%	$221.5708	$221.57	$221.55	$221.60
Purchase #5	$143.38	6.617%	$152.8675	$152.87	$152.85	$152.90
Purchase #6	$133.40	6.474%	$142.0363	$142.04	$142.05	$142.00
Purchase #7	$38.86	3.315%	$40.1482	$40.15	$40.15	$40.10
7 purchase totals =	$910.23		$987.5699	$987.58	$987.55	$987.50