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	$27.79	12.479%	$31.2579	$31.26	$31.25	$31.30
Purchase #2	$32.89	4.374%	$34.3286	$34.33	$34.35	$34.30
Purchase #3	$66.48	8.815%	$72.3402	$72.34	$72.35	$72.30
Purchase #4	$13.29	10.271%	$14.655	$14.66	$14.65	$14.70
Purchase #5	$116.86	13.824%	$133.0147	$133.01	$133.00	$133.00
Purchase #6	$29.56	10.180%	$32.5692	$32.57	$32.55	$32.60
Purchase #7	$128.54	6.482%	$136.872	$136.87	$136.85	$136.90
7 purchase totals =	$415.41		$455.0376	$455.04	$455.00	$455.10