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	$173.59	3.670%	$179.9608	$179.96	$179.95	$180.00
Purchase #2	$57.26	5.564%	$60.4459	$60.45	$60.45	$60.40
Purchase #3	$73.56	9.167%	$80.3032	$80.30	$80.30	$80.30
Purchase #4	$121.98	11.794%	$136.3663	$136.37	$136.35	$136.40
Purchase #5	$52.91	8.594%	$57.4571	$57.46	$57.45	$57.50
Purchase #6	$50.64	7.807%	$54.5935	$54.59	$54.60	$54.60
Purchase #7	$241.89	7.139%	$259.1585	$259.16	$259.15	$259.20
7 purchase totals =	$771.83		$828.2853	$828.29	$828.25	$828.40