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	$85.86	5.728%	$90.7781	$90.78	$90.80	$90.80
Purchase #2	$212.85	8.257%	$230.425	$230.43	$230.45	$230.40
Purchase #3	$89.35	10.629%	$98.847	$98.85	$98.85	$98.80
Purchase #4	$232.51	10.860%	$257.7606	$257.76	$257.75	$257.80
Purchase #5	$196.71	8.538%	$213.5051	$213.51	$213.50	$213.50
Purchase #6	$102.25	7.489%	$109.9075	$109.91	$109.90	$109.90
Purchase #7	$214.85	5.443%	$226.5443	$226.54	$226.55	$226.50
7 purchase totals =	$1,134.38		$1,227.7676	$1,227.78	$1,227.80	$1,227.70