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	$11.44	9.792%	$12.5602	$12.56	$12.55	$12.60
Purchase #2	$129.28	7.700%	$139.2346	$139.23	$139.25	$139.20
Purchase #3	$50.50	4.844%	$52.9462	$52.95	$52.95	$52.90
Purchase #4	$25.75	7.371%	$27.648	$27.65	$27.65	$27.60
Purchase #5	$137.90	9.736%	$151.3259	$151.33	$151.35	$151.30
Purchase #6	$104.43	13.397%	$118.4205	$118.42	$118.40	$118.40
Purchase #7	$228.49	13.531%	$259.407	$259.41	$259.40	$259.40
7 purchase totals =	$687.79		$761.5424	$761.55	$761.55	$761.40