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	$50.54	8.400%	$54.7854	$54.79	$54.80	$54.80
Purchase #2	$131.37	12.544%	$147.8491	$147.85	$147.85	$147.80
Purchase #3	$85.40	4.202%	$88.9885	$88.99	$89.00	$89.00
Purchase #4	$78.51	4.539%	$82.0736	$82.07	$82.05	$82.10
Purchase #5	$231.79	11.108%	$257.5372	$257.54	$257.55	$257.50
Purchase #6	$211.28	7.808%	$227.7767	$227.78	$227.80	$227.80
Purchase #7	$21.39	5.268%	$22.5168	$22.52	$22.50	$22.50
7 purchase totals =	$810.28		$881.5273	$881.54	$881.55	$881.50