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	$34.53	6.291%	$36.7023	$36.70	$36.70	$36.70
Purchase #2	$125.56	13.658%	$142.709	$142.71	$142.70	$142.70
Purchase #3	$106.64	5.746%	$112.7675	$112.77	$112.75	$112.80
Purchase #4	$242.89	5.746%	$256.8465	$256.85	$256.85	$256.80
Purchase #5	$74.67	7.800%	$80.4943	$80.49	$80.50	$80.50
Purchase #6	$116.53	12.466%	$131.0566	$131.06	$131.05	$131.10
Purchase #7	$122.35	7.672%	$131.7367	$131.74	$131.75	$131.70
7 purchase totals =	$823.17		$892.3129	$892.32	$892.30	$892.30