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	$52.82	3.369%	$54.5995	$54.60	$54.60	$54.60
Purchase #2	$171.81	12.151%	$192.6866	$192.69	$192.70	$192.70
Purchase #3	$26.90	3.822%	$27.9281	$27.93	$27.95	$27.90
Purchase #4	$239.61	8.314%	$259.5312	$259.53	$259.55	$259.50
Purchase #5	$171.45	9.662%	$188.0155	$188.02	$188.00	$188.00
Purchase #6	$164.48	4.838%	$172.4375	$172.44	$172.45	$172.40
Purchase #7	$179.50	9.339%	$196.2635	$196.26	$196.25	$196.30
7 purchase totals =	$1,006.57		$1,091.4619	$1,091.47	$1,091.50	$1,091.40