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	$168.51	13.150%	$190.6691	$190.67	$190.65	$190.70
Purchase #2	$205.65	10.383%	$227.0026	$227.00	$227.00	$227.00
Purchase #3	$31.50	13.662%	$35.8035	$35.80	$35.80	$35.80
Purchase #4	$122.33	7.351%	$131.3225	$131.32	$131.30	$131.30
Purchase #5	$133.79	4.187%	$139.3918	$139.39	$139.40	$139.40
Purchase #6	$84.73	5.673%	$89.5367	$89.54	$89.55	$89.50
Purchase #7	$61.94	7.224%	$66.4145	$66.41	$66.40	$66.40
7 purchase totals =	$808.45		$880.1407	$880.13	$880.10	$880.10