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	$199.74	12.710%	$225.127	$225.13	$225.15	$225.10
Purchase #2	$131.66	11.234%	$146.4507	$146.45	$146.45	$146.50
Purchase #3	$67.46	13.296%	$76.4295	$76.43	$76.45	$76.40
Purchase #4	$74.48	10.300%	$82.1514	$82.15	$82.15	$82.20
Purchase #5	$85.83	5.524%	$90.5712	$90.57	$90.55	$90.60
Purchase #6	$209.99	3.577%	$217.5013	$217.50	$217.50	$217.50
Purchase #7	$44.81	5.173%	$47.128	$47.13	$47.15	$47.10
7 purchase totals =	$813.97		$885.3591	$885.36	$885.40	$885.40