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	$76.69	6.706%	$81.8328	$81.83	$81.85	$81.80
Purchase #2	$201.32	4.245%	$209.866	$209.87	$209.85	$209.90
Purchase #3	$54.33	12.751%	$61.2576	$61.26	$61.25	$61.30
Purchase #4	$40.67	4.606%	$42.5433	$42.54	$42.55	$42.50
Purchase #5	$110.78	3.626%	$114.7969	$114.80	$114.80	$114.80
Purchase #6	$64.65	4.113%	$67.3091	$67.31	$67.30	$67.30
Purchase #7	$131.55	9.368%	$143.8736	$143.87	$143.85	$143.90
7 purchase totals =	$679.99		$721.4793	$721.48	$721.45	$721.50