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	$43.85	4.657%	$45.8921	$45.89	$45.90	$45.90
Purchase #2	$30.98	4.383%	$32.3379	$32.34	$32.35	$32.30
Purchase #3	$120.90	13.284%	$136.9604	$136.96	$136.95	$137.00
Purchase #4	$156.77	9.345%	$171.4202	$171.42	$171.40	$171.40
Purchase #5	$120.52	6.782%	$128.6937	$128.69	$128.70	$128.70
Purchase #6	$115.48	13.491%	$131.0594	$131.06	$131.05	$131.10
Purchase #7	$97.49	3.258%	$100.6662	$100.67	$100.65	$100.70
7 purchase totals =	$685.99		$747.0299	$747.03	$747.00	$747.10