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	$96.76	3.597%	$100.2405	$100.24	$100.25	$100.20
Purchase #2	$156.35	5.874%	$165.534	$165.53	$165.55	$165.50
Purchase #3	$174.35	12.431%	$196.0234	$196.02	$196.00	$196.00
Purchase #4	$100.74	7.847%	$108.6451	$108.65	$108.65	$108.60
Purchase #5	$7.25	3.859%	$7.5298	$7.53	$7.55	$7.50
Purchase #6	$195.83	12.189%	$219.6997	$219.70	$219.70	$219.70
Purchase #7	$47.96	9.610%	$52.569	$52.57	$52.55	$52.60
7 purchase totals =	$779.24		$850.2415	$850.24	$850.25	$850.10