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	$129.32	5.729%	$136.7287	$136.73	$136.75	$136.70
Purchase #2	$113.33	8.565%	$123.0367	$123.04	$123.05	$123.00
Purchase #3	$135.87	8.551%	$147.4882	$147.49	$147.50	$147.50
Purchase #4	$194.33	7.750%	$209.3906	$209.39	$209.40	$209.40
Purchase #5	$93.71	10.581%	$103.6255	$103.63	$103.65	$103.60
Purchase #6	$152.82	12.275%	$171.5787	$171.58	$171.60	$171.60
Purchase #7	$24.52	4.353%	$25.5874	$25.59	$25.60	$25.60
7 purchase totals =	$843.90		$917.4358	$917.45	$917.55	$917.40