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	$174.98	7.333%	$187.8113	$187.81	$187.80	$187.80
Purchase #2	$225.86	8.754%	$245.6318	$245.63	$245.65	$245.60
Purchase #3	$39.37	8.398%	$42.6763	$42.68	$42.70	$42.70
Purchase #4	$187.30	7.524%	$201.3925	$201.39	$201.40	$201.40
Purchase #5	$100.96	3.723%	$104.7187	$104.72	$104.70	$104.70
Purchase #6	$81.45	9.718%	$89.3653	$89.37	$89.35	$89.40
Purchase #7	$90.87	9.495%	$99.4981	$99.50	$99.50	$99.50
7 purchase totals =	$900.79		$971.0940	$971.10	$971.10	$971.10