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	$64.61	13.692%	$73.4564	$73.46	$73.45	$73.50
Purchase #2	$138.34	3.715%	$143.4793	$143.48	$143.50	$143.50
Purchase #3	$95.81	9.309%	$104.729	$104.73	$104.75	$104.70
Purchase #4	$31.70	11.440%	$35.3265	$35.33	$35.35	$35.30
Purchase #5	$187.62	10.113%	$206.594	$206.59	$206.60	$206.60
Purchase #6	$239.37	6.275%	$254.3905	$254.39	$254.40	$254.40
Purchase #7	$50.44	8.635%	$54.7955	$54.80	$54.80	$54.80
7 purchase totals =	$807.89		$872.7712	$872.78	$872.85	$872.80