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	$130.53	8.784%	$141.9958	$142.00	$142.00	$142.00
Purchase #2	$177.53	6.871%	$189.7281	$189.73	$189.75	$189.70
Purchase #3	$70.27	12.104%	$78.7755	$78.78	$78.80	$78.80
Purchase #4	$122.93	11.310%	$136.8334	$136.83	$136.85	$136.80
Purchase #5	$155.58	3.789%	$161.4749	$161.47	$161.45	$161.50
Purchase #6	$91.73	9.310%	$100.2701	$100.27	$100.25	$100.30
Purchase #7	$90.54	9.188%	$98.8588	$98.86	$98.85	$98.90
7 purchase totals =	$839.11		$907.9366	$907.94	$907.95	$908.00