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	$97.52	3.468%	$100.902	$100.90	$100.90	$100.90
Purchase #2	$35.61	5.161%	$37.4478	$37.45	$37.45	$37.40
Purchase #3	$240.42	5.421%	$253.4532	$253.45	$253.45	$253.50
Purchase #4	$126.90	3.458%	$131.2882	$131.29	$131.30	$131.30
Purchase #5	$135.25	6.589%	$144.1616	$144.16	$144.15	$144.20
Purchase #6	$161.48	12.528%	$181.7102	$181.71	$181.70	$181.70
Purchase #7	$8.41	5.229%	$8.8498	$8.85	$8.85	$8.80
7 purchase totals =	$805.59		$857.8128	$857.81	$857.80	$857.80