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	$141.52	12.706%	$159.5015	$159.50	$159.50	$159.50
Purchase #2	$186.46	6.572%	$198.7142	$198.71	$198.70	$198.70
Purchase #3	$219.60	11.333%	$244.4873	$244.49	$244.50	$244.50
Purchase #4	$50.35	9.501%	$55.1338	$55.13	$55.15	$55.10
Purchase #5	$164.74	7.520%	$177.1284	$177.13	$177.15	$177.10
Purchase #6	$243.45	5.505%	$256.8519	$256.85	$256.85	$256.90
Purchase #7	$37.48	5.436%	$39.5174	$39.52	$39.50	$39.50
7 purchase totals =	$1,043.60		$1,131.3345	$1,131.33	$1,131.35	$1,131.30