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	$185.89	3.227%	$191.8887	$191.89	$191.90	$191.90
Purchase #2	$39.29	3.424%	$40.6353	$40.64	$40.65	$40.60
Purchase #3	$145.32	6.504%	$154.7716	$154.77	$154.75	$154.80
Purchase #4	$198.47	3.611%	$205.6368	$205.64	$205.65	$205.60
Purchase #5	$54.48	9.559%	$59.6877	$59.69	$59.70	$59.70
Purchase #6	$62.96	12.758%	$70.9924	$70.99	$71.00	$71.00
Purchase #7	$42.26	13.537%	$47.9807	$47.98	$48.00	$48.00
7 purchase totals =	$728.67		$771.5932	$771.60	$771.65	$771.60