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	$131.97	6.299%	$140.2828	$140.28	$140.30	$140.30
Purchase #2	$228.89	5.360%	$241.1585	$241.16	$241.15	$241.20
Purchase #3	$100.87	12.564%	$113.5433	$113.54	$113.55	$113.50
Purchase #4	$141.82	13.199%	$160.5388	$160.54	$160.55	$160.50
Purchase #5	$136.27	6.788%	$145.52	$145.52	$145.50	$145.50
Purchase #6	$92.47	11.419%	$103.0291	$103.03	$103.05	$103.00
Purchase #7	$70.48	11.592%	$78.65	$78.65	$78.65	$78.70
7 purchase totals =	$902.77		$982.7225	$982.72	$982.75	$982.70