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	$158.59	12.245%	$178.0093	$178.01	$178.00	$178.00
Purchase #2	$91.80	7.653%	$98.8255	$98.83	$98.85	$98.80
Purchase #3	$200.83	12.797%	$226.5302	$226.53	$226.55	$226.50
Purchase #4	$82.47	8.136%	$89.1798	$89.18	$89.20	$89.20
Purchase #5	$137.39	3.588%	$142.3196	$142.32	$142.30	$142.30
Purchase #6	$30.89	4.738%	$32.3536	$32.35	$32.35	$32.40
Purchase #7	$60.70	11.818%	$67.8735	$67.87	$67.85	$67.90
7 purchase totals =	$762.67		$835.0915	$835.09	$835.10	$835.10